Thanks for the feedback.
The repository will be mirrored to github soon. In the meantime the general the process is:
Clone the repository from https://stash.kopano.io/
Commit and sign your work (git commit -s).
Upload commits to a git store of your choosing, or export the series as a patchset using git format-patch.
Send the patch(es) or git link to contributing@kopano.io and we will consider the submission.