NEXT: Document the process for submitting PRs

[martinb3]

Per @karmi's email, it should be:

• Create a branch directly in this repo or a fork (if you don't have push access), something like karmi/install_from_deb
• Create an issue/open a PR
• Close (and reference) issues by the Closes #XXX / Fixes #XXX notation in the commit message
• Keep pushing commits to the initial branch
• When everything is ready for merge, clean up the branch (rebase with next to synchronize, squash, edit commits, etc) and merge it into next (or master, when the time comes to move over to the next branch permanently)
• When it's couple of commits which are to be considered a logical whole, merge it with --no-ff switch, so it's indicated in the Git history
• Do not use the "merge button", since it doesn't do a fast-forward merge (see previous item)