add server-side hook: proc-receive

Author: Li Linchao

book/08-customizing-git/sections/hooks.asc

@@ -111,6 +111,14 @@ The first script to run when handling a push from a client is `pre-receive`.
 It takes a list of references that are being pushed from stdin; if it exits non-zero, none of them are accepted.
 You can use this hook to do things like make sure none of the updated references are non-fast-forwards, or to do access control for all the refs and files they're modifying with the push.
 
+===== `proc-receive`
+
+The `proc-receive` script is quite different from other server-side scripts, it is invoked by git push process, but can change the workflow or process between `pre-reveive` and `post-receive` hook.
+This's because if the upcoming update references match the specified reference pattern, which can be configured by `receive.procReceiveRefs`, then `proc-receive` will take over the whole flow
+after `pre-receive`, then ignore the `update` script. It can decide to create, update or rename new reference, or even fallback to previous process.
+In other word, it can outsource reference processing flow, this give a system administrator to customize very useful policy for pushing workflow, such as Gerrit-like workflow in native Git.
+This script runs once at push process, and can stop the push process.
+
 ===== `update`
 
 The `update` script is very similar to the `pre-receive` script, except that it's run once for each branch the pusher is trying to update.