Add git-annex docs

CHANGELOG-EE

@@ -6,6 +6,7 @@ v 7.8.0
   - Added Github Enterprise importer
   - When project has MR rebase enabled, MR will have rebase checkbox selected by default
   - Minor UI fixes for sidebar navigation
+  - Manage large binaries with git annex
 
 v 7.7.0
   - Added custom header logo support (Drew Blessing)

doc/workflow/README.md

@@ -13,3 +13,4 @@
 - [Project importing from GitLab.com to your private GitLab instance](import_projects_from_gitlab_com.md)
 - [Protected branches](protected_branches.md)
 - [Web Editor](web_editor.md)
+- [Manage large binaries with git annex](git_annex.md)

doc/workflow/git_annex.md

+# Git annex
+
+The biggest limitation of git compared to some older centralized version control systems has been the maximum size of the repositories.
+The general recommendation is to not have git repositories larger than 1GB to preserve performance.
+Although GitLab has no limit (some repositories in GitLab are over 50GB!) we subscribe to the advise to keep repositories as small as you can.
+
+Not being able to version control large binaries is a big problem for many larger organizations.
+Video, photo's, audio, compiled binaries and many other types of files are too large.
+As a workaround, people keep artwork-in-progress in a Dropbox folder and only check in the final result.
+This results in using outdated files, not having a complete history and the risk of losing work.
+
+This problem is solved by integrating the awesome [git-annex](https://git-annex.branchable.com/).
+Git-annex allows managing large binaries with git, without checking the contents into git.
+You check in only a symlink that contains the SHA-1 of the large binary.
+If you need the large binary you can sync it from the GitLab server over rsync, a very fast file copying tool.
+
+<!-- more -->
+
+## Using GitLab Annex
+
+For example, if you want to upload a very large file and check it into your Git repository:
+
+```bash
+git clone git@gitlab.example.com:group/project.git
+git annex init 'My Laptop'            # initialize the annex project
+cp ~/tmp/debian.iso ./                # copy a large file into the current directory
+git annex add .                       # add the large file to git annex
+git commit -am"Added Debian iso"      # commit the file meta data
+git annex sync --content              # sync the git repo and large file to the GitLab server
+```
+
+Downloading a single large file is also very simple:
+
+```bash
+git clone git@gitlab.example.com:group/project.git
+git annex sync                        # sync git branches but not the large file
+git annex get debian.iso              # download the large file
+```
+
+To download all files:
+
+```bash
+git clone git@gitlab.example.com:group/project.git
+git annex sync --content              # sync git branches and download all the large files
+```
+
+You don't have to setup git-annex on a separate server or add annex remotes to the repository.
+Git-annex without GitLab gives everyone that can access the server access to the files of all projects.
+GitLab annex ensures you can only acces files of projects you work on (developer, master or owner role).
+
+## How it works
+
+Internally GitLab uses [GitLab Shell](https://gitlab.com/gitlab-org/gitlab-shell) to handle ssh access and this was a great integration point for git-annex.
+We've added a setting to GitLab Shell so you can disable GitLab Annex support if you don't want it.
+
+You'll have to use ssh style links for to git remote to your GitLab server instead of https style links.