Move some of the verbose PR description instructions into PR comments

[lihaoyi]

Currently, the verbose PR descriptions end up in the commit history by anyone using Squash and Merge on Github, which is a relatively common workflow for those wanting to maintain linear histories:

To avoid this, we can move the bulk of the instructions/about/FAQ/etc. in a PR comment, leaving only the core Scala Stweward: update foo bar from v1 to v2 text in the PR description

[fthomas]

I cannot reproduce this. For example, fthomas/status-page@dc7716b and scala-steward-org/test-repo-1@c4e334f have been "Squash and merge"-ed via GitHub and both do not contain the PR body.

[lihaoyi]

@fthomas whether it contains the PR body or not is configurable in repo settings.

In my org, we put a lot more effort into reviewing at PR granularity rather than commit granularity, so the focus is on readable PR descriptions that are then squashed into the single commit description when merging. So we configure the repo to use the PR description as the message. This works great for almost all PRs, except for Scala Steward. And that can be fixed if Scala Steward were tweaked as described in this ticket

[lihaoyi]

FYI here's the repo setting if you haven't seen it