Update content for 4.0, part 2

[trwnh]

Follow-up to #991

Preview: https://master--mastodocs.netlify.app/

[MFTabriz]

@Gargron @trwnh Squashing the commits while stripping the PR author’s info/attribution from the commit history does not look like a GFDL-compliant approach to me.

[nemobis]

Squashing the commits while stripping the PR author’s info/attribution from the commit history does not look like a GFDL-compliant approach

Currently this repository doesn't seem to state the copyright holders anywhere in the file contents, which means preserving git history is probably necessary at the moment for attribution, but as for this specific commit I wouldn't be so sure because it was probably purchased by Mastodon gGmbH, presumably with a copyright assignment or even a work-for-hire arrangement.