Use this weird trick to make code reviews easier, faster and more effective

In the section "Merging stacked Pull Requests" is mentioned:

> "...we must start merging from the top, i.e., the last opened pull request. Doing otherwise will result in a state where we cannot merge our pull requests anymore."

I think with the idea of PR re-targeting[1] that section could be enriched just to cover premature merging, accidentally or needed.

[1] https://twitter.com/getupleveled/status/1300714078198018049?...