Symlinked hooks aren't executed

This recently changed on the Gitaly side, but now spotted this in the
docs for the next release. Updated to be more precise, and to signal
users should not want control over this specific hook location.

doc/administration/custom_hooks.md

@@ -60,7 +60,7 @@ installations, this can be set in `gitlab-shell/config.yml`.
 
 The hooks are searched and executed in this order:
 
-1. `<project>.git/hooks/` - symlink to `gitlab-shell/hooks` global dir
+1. `gitlab-shell/hooks` directory as known to Gitaly
 1. `<project>.git/hooks/<hook_name>` -  executed by `git` itself, this is `gitlab-shell/hooks/<hook_name>`
 1. `<project>.git/custom_hooks/<hook_name>` - per project hook (this is already existing behavior)
 1. `<project>.git/custom_hooks/<hook_name>.d/*` - per project hooks