This makes two changes to the documentation:

* Adds a comment in the release notes about the ability to
  quote primitive chars and strings in TH (see D1054)
* Removes an outdated comment in the users' guide about TH not
  being able to handle `PartialTypeSignatures` (which was fixed in
  D1048)

Reviewers: goldfire, austin, simonpj, bgamari

Reviewed By: simonpj, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1125