Add a release blurb and fixup changes for 2021.2

[seanbudd]

Description

Adds a release blurb and proposes some changes to the changelog and userGuide.

Testing strategy

I performed a review of git diff release-2021.1 userDocsChanges2021.2 user_docs/en/*.t2t.

The build artifact for changes.html and userGuide.html should be checked before merging.

Code Review Checklist:

• Pull Request description is up to date.
• Unit tests.
• System (end to end) tests.
• Manual testing.
• User Documentation.
• Change log entry.
• Context sensitive help for GUI changes.
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers

[feerrenrut]

newer than

Shouldn't this be "when using x or later"?

[seanbudd]

Actually yes, that is the case as far as I'm aware. Before I fix this (across the rest of the documentation) I'm going to check this via the release preview channel for WIN1021H2. I have confirmed the previous release of Windows works, Windows 10 21H1.

[seanbudd]

The change of behaviour occurred in an insiders build, #12491 reports this change of behaviour for a build sometime after the WIN10 21H2 build number. I am yet to be able to test WIN10 21H2 preview (haven't been offered the update). It would be good if someone can confirm whether or not screen curtain works with the WIN10 21H2 preview, but for now I will move forward to say "when using it or later" due to being uncertain.

[michaelDCurran]

This looks good to me.

[feerrenrut]

Overall I think this is fine.

Just a couple of ideas, trying to make the language for the screen curtain edge cases as simple as possible.

[seanbudd]

@feerrenrut - I've rephrased this message across both files now. Let me know what you think.