Add link to source code to Community page

Just saw someone at RedHat struggle to reach our source code, he looked at the community page, that makes sense.

As the first item on https://about.gitlab.com/community/ add a link to https://gitlab.com/gitlab-org/gitlab-ce/tree/master#README

Fixed with https://gitlab.com/gitlab-com/www-gitlab-com/commit/2f39deb6460ad17c31812b72688560b5b7ec1552

Status changed to closed

mentioned in commit 4d8745bf