Update v3 to v4 how-to re: installer version (442)

[Hooverdan96]

Fixes #442.

This pull request's proposal

Changes to be committed: modified: v3_to_v4.rst

• update installer reference
• some rewording/extension
• fixed some typos

Checklist

• [X] With the proposed changes no Sphinx errors or warnings are generated.
• [X] I have added my name to the AUTHORS file, if required (descending alphabetical order).

[Hooverdan96]

linkcheck failure, due to known broken link (addressed pull request #447) (line 97) broken https://btrfs.wiki.kernel.org/index.php/Glossary - 404 Client Error: Not Found for url: https://archive.kernel.org/oldwiki/btrfs.wiki.kernel.org/index.php/Glossary.html

[Hooverdan96]

All changes accepted!

[phillxnet]

PR product PRODUCTION published.