minor additions to README.md

[IzzySoft]

Some minor amendments:

• pruning alternatives: Mastodon also offers this itself now (see preferences › Automated post deletion in the WebIF)
• alternative viewers: mav-z is another nice archive viewer

Plus some "space cleanups" (consistency: replace the few tabs by spaces, remove obsolete trailing spaces)

Ready for merge – unless you want to update stating forget is no longer maintained (just integrate it as "suggested change" if you like :wink:).

[kensanata]

I removed 'forget' since it no longer works and the maintainer does not intend to bring it back.

[IzzySoft]

I removed 'forget' since it no longer works and the maintainer does not intend to bring it back.

Makes sense. I didn't because someone might fork it – but well, might or not, it's not maintained now. Thanks!