[nayuos] Improve readme

software/nayuos/README.md

 # NayuOS
 
-This is a SlapOS recipe to build NayuOS. It needs to be put in the <code>/srv/slapgrid/\<part\>/srv/runner/project/slapos/software/</code> directory. The created directory is called <code>\<nayuos_build_dirname\></code> in this documentation.
+This is a SlapOS recipe to build NayuOS.
 
 ## License
 
@@ -8,43 +8,61 @@ GPL v2 or later
 
 ## Requirements
 
-*   sudo on the host (for now)
-*   some environment variables need to be authorized to be propagated when cros_sdk calls sudo:
+*   sudo on the host
+*   environment variables need to be authorized to be propagated when cros_sdk calls sudo: `: Defaults        env_keep += "CROS_CACHEDIR DEPOT_TOOLS"`
+*   slapuser with sudo rights to execute the cros_sdk scripts (needed to access the chroot environment provided by Chromium OS)
+in /etc/sudoers (replace slapuser9 by your user, and release-R48-7647.B by the release you have chosen): `: slapuser9    ALL=NOPASSWD: /srv/slapgrid/slappart9/srv/runner/instance/slappart0/parts/chromiumos/release-R48-7647.B/chromite/bin/cros_sdk, /srv/slapgrid/slappart9/srv/runner/instance/slappart0/wrapper_bin/wrapper_cros_sdk, /bin/kill`
 
-: Defaults        env_keep += "CROS_CACHEDIR DEPOT_TOOLS"
+It's useful to have the right to kill cros_sdk processes, when needed. ;)
 
-*   slapuser with sudo rights to execute the cros_sdk scripts (needed to access the chroot environment provided by Chromium OS)
-in /etc/sudoers (replace slapuser9 by your user, and release-R48-7647.B by the release you have chosen):
+## Technical notes
 
-: slapuser9    ALL=NOPASSWD: /srv/slapgrid/slappart9/srv/runner/instance/slappart0/parts/chromiumos/release-R48-7647.B/chromite/bin/cros_sdk, /srv/slapgrid/slappart9/srv/runner/instance/slappart0/wrapper_bin/wrapper_cros_sdk, /bin/kill
+After any change to the build process it is necessary to delete (using sudo)
+the building environment at `~/srv/runner/instance/slappart0/parts/chromiumos/<TAG>`.
+
+BEWARE that the web runner is serving images for the [official website](https://nayuos.nexedi.com).
+
+NayuOS and ChromiumOS is "just" a version of Gentoo. Thus it uses `ebuild` packages
+and anything installable in Gentoo can be installed to NayuOS too. Of course only
+during OS build phase and one has to count with limited space.
+
+### Upgrading (building new image)
+
+Please read **Requirements** section carefully. After selecting your desired 
+`release` from the list <https://chromium.googlesource.com/chromiumos/manifest/+refs>
+it is **necessary** to add `sudo` rules for that release as shown there.
 
-It's useful to have the right to kill cros_sdk processes, when needed. ;)
 
 ## Input
+
 In the vifib parameters (softinst\<nb\>.host.vifib.net \> Services \> Parameters):
 
-*   board / ex: peppy, swanky, ... (choosing daisy will accept all licenses for the daisy board build only, in order to use Mali drivers, see [chromium mailing list](https://groups.google.com/a/chromium.org/forum/#!topic/chromium-os-dev/Pf9ZG2itxWM))
-*   branch / ex: release-R46-7390.B (you can find the release in the [Chromium OS source tree](https://chromium.googlesource.com/chromiumos/manifest/+refs))
-*   keep_cache / yes|no (choosing "no" saves about 15Go of disk space per board, choosing "yes" will makes next build faster and less expensive in term of needed ressources because of not rebuilding everything)
+*   **board** / ex: peppy, swanky, ... (choosing daisy will accept all licenses for the daisy board build only, in order to use Mali drivers, see [chromium mailing list](https://groups.google.com/a/chromium.org/forum/#!topic/chromium-os-dev/Pf9ZG2itxWM))
+*   **branch** / ex: release-R46-7390.B (you can find the release in the [Chromium OS source tree](https://chromium.googlesource.com/chromiumos/manifest/+refs))
+*   **keep_cache** / yes|no (choosing "no" saves about 15Go of disk space per board, choosing "yes" will makes next build faster and less expensive in term of needed ressources because of not rebuilding everything)
 
 
 ## Output
-The image will be produced in:
-<code>/srv/slapgrid/\<part\>/srv/runner/instance/\<inst_part\>/parts/chromiumos/images/</code>
-and the logs are in:
-<code>/srv/slapgrid/\<part\>/srv/runner/instance/\<inst_part\>/var/log/cros_sources_dl.log</code> and <code>/srv/slapgrid/\<part\>/srv/runner/instance/\<inst_part\>/var/log/cros_build.log</code>
 
-The script that download the sources and build is located in
-<code>/srv/slapgrid/\<part\>/srv/runner/instance/\<inst_part\>/etc/run</code>
+Software release produces a build script `<instance_partition>/etc/run/cros_full_build`.
+
+Build produces
+
+*  Image: `<instance_partition>/parts/chromiumos/images/`
+*  Compilation logs: `<instance_partition>/var/log/cros_sources_dl.log`
+*  Build logs: `<instance_partition>/var/log/cros_build.log`
+
 
 ## External documents
 
-*   [ <code>repo</code> command reference ](https://source.android.com/source/using-repo.html)
-*   [ NayuOS official website ](https://www.nayuos.com)
+*   [ `repo` command reference ](https://source.android.com/source/using-repo.html)
+*   [ NayuOS official website ](https://nayuos.nexedi.com)
 *   [ crouton for chroot ](https://github.com/dnschneid/crouton) ([warning about verified boot](https://github.com/dnschneid/crouton/blob/2a1fc9da380650f47e2bcf37d00962bfb68c4830/installer/main.sh#L517-L536))
 
 ## Notes for possible improvements
+
 *   [ Running virtual machines on your chromebook ](https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/running-virtual-machines-on-your-chromebook)
 *   to have a more common User Agent (the one of ChromiumOS/NayuOS is quite rare and identifies the user, see [studies of the EFF](https://panopticlick.eff.org/static/browser-uniqueness.pdf)), it seems possible to change the User-Agent flag for guest mode in the getOffTheRecord function, and adding a line (key "kUserAgent" , value "some common user agent" string). Then rebuild Chromium and [add it to NayuOS](https://www.chromium.org/chromium-os/developer-guide#TOC-Making-changes-to-the-Chromium-web-).
 *   remove need of root priviledge for entering the chroot, maybe by using fakeroot in 'scripts/wrapper_sudo.in'?
 *   change more options on Chromium OS "Privacy" part by default: there are [a few options](https://support.google.com/chromebook/answer/114836) which still use Google services
+*   provide ChromiumOS package manager [ chromebrew ](https://skycocker.github.io/chromebrew/) by default