website: Add pre-commit doc to Contributing page

Change-Id: Ie95078bb38208c0ba3f51dc34b4a788cc9aaa40f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/62111
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
1 file changed