Remove broken link in `README.md`

[abooij]

trafficstars

It seems like the trunk branch got renamed.

• [ ] Did you add a new feature to hpack?
  • [ ] Did you add an acceptance test for that new feature to test/EndToEndSpec.hs?

[sol]

This change makes sense. However, we currently don't produce binary distributions. So this is something we need to do to make this change meaningful.

[abooij]

@sol How about just removing the link, then? I've updated the PR.

[mpilgrem]

@abooij, I made a change to put 'currently' in the context of 'previously'. I also tidied-up the commit history, in preparation for merging.