Correcting using git doc link

This docs page has been removed on the dev_4_4 branch of OMERO (now in the new contributing docs section on the develop branch only), so this changes the link to a hard-coded one to avoid linking across branches. Should make the bf-docs-merge-stable build green again.

May need rebasing to dev_5_0 (I need to check) but will NOT need rebasing to develop.