added development task workflow

I think the main verb here is "merges".  Suggested:  Tester accepts and merges the pull request, by pressing the green merge button on the pull request, or via the command line.   If the button is not green and warns that a manual merge is necessary, then the developer likely did not rebase recently.  The developer will then update the branch to achieve a green merge button, and resubmit to the tester.