Custom git hook documentation

doc/README.md

@@ -16,6 +16,7 @@
 - [Install](install/README.md) Requirements, directory structures and manual installation.
 - [Integration](integration/README.md) How to integrate with systems such as JIRA, Redmine, LDAP and Twitter.
 - [Raketasks](raketasks/README.md) Explore what GitLab has in store for you to make administration easier.
+- [Custom git hooks](hooks/custom_hooks.md) Custom git hooks (on the filesystem) for when web hooks aren't enough.
 - [System hooks](system_hooks/system_hooks.md) Let GitLab notify you when certain management tasks need to be carried out.
 - [Security](security/README.md) Learn what you can do to further secure your GitLab instance.
 - [Update](update/README.md) Update guides to upgrade your installation.

doc/hooks/custom_hooks.md

+# Custom Git Hooks
+
+**Note: Custom git hooks must be configured on the filesystem of the GitLab
+server. Only GitLab server administrators will be able to complete these tasks.
+Please explore webhooks as an option if you do not have filesystem access.**
+
+Git natively supports hooks that are executed on different actions.
+Examples of server-side git hooks include pre-receive, post-receive, and update.
+See
+[Git SCM Server-Side Hooks](http://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks#Server-Side-Hooks)
+for more information about each hook type.
+
+As of gitlab-shell version 2.2.0 (which requires GitLab 7.5+), GitLab
+administrators can add custom git hooks to any GitLab project.
+
+## Setup
+
+Normally, git hooks are placed in the repository or project's `hooks` directory.
+GitLab creates a symlink from each project's `hooks` directory to the
+gitlab-shell `hooks` directory for ease of maintenance between gitlab-shell
+upgrades. As such, custom hooks are implemented a little differently. Behavior
+is exactly the same once the hook is created, though. Follow these steps to
+set up a custom hook.
+
+1. Pick a project that needs a custom git hook.
+1. On the GitLab server, navigate to the project's repository directory.
+For a manual install the path is usually 
+`/home/git/repositories/<group>/<project>.git`. For Omnibus installs the path is
+usually `/var/opt/gitlab/git-data/repositories/<group>/<project>.git`.
+1. Create a new directory in this location called `custom_hooks`.
+1. Inside the new `custom_hooks` directory, create a file with a name matching
+the hook type. For a pre-receive hook the file name should be `pre-receive` with
+no extension.
+1. Make the hook file executable and make sure it's owned by git.
+1. Write the code to make the git hook function as expected. Hooks can be
+in any language. Ensure the 'shebang' at the top properly reflects the language
+type. For example, if the script is in Ruby the shebang will probably be
+`#!/usr/bin/env ruby`.
+
+That's it! Assuming the hook code is properly implemented the hook will fire
+as appropriate.