[PATCH/RFC] Documentation/git-gc.txt: add reference to githooks

[Chris Packham <judge.packham@gmail.com>]

This advertises the existence of the 'pre-auto-gc' hook and adds a cross
reference to where the hook is documented.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
---
I had to go fishing in the code to find out about the pre-auto-gc hook. From
reading the git-gc man page it wasn't obvious to me that there would be a hook
for 'git gc --auto'. The relevant config variables are mentioned so it seems
logical to mention the hooks also. The only precedent I found for this was in
the git-commit man page which has a section listing the hooks that are
available.

 Documentation/git-gc.txt |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/Documentation/git-gc.txt b/Documentation/git-gc.txt
index a9e0882..a514c52 100644
--- a/Documentation/git-gc.txt
+++ b/Documentation/git-gc.txt
@@ -137,6 +137,11 @@ If you are expecting some objects to be collected and they aren't, check
 all of those locations and decide whether it makes sense in your case to
 remove those references.
 
+HOOKS
+-----
+This command can run `pre-auto-gc` hook.  See linkgit:githooks[5] for more
+information.
+
 SEE ALSO
 --------
 linkgit:git-prune[1]
-- 
1.7.1