[Tails-dev] [review'n'merge] screen keyboard documentation

Hello, it's a branch for testing to fix few errors in screen keyboard
documentation.

Please review and merge.

Repo: https://git-tails.immerda.ch/xin/tails/
Branch: fix_doc_3.2
Last Commit: 083cece9948db5df2b655b0039fecf3ef9208ce3

Cheers.
xin