Clean up of Pre-installation Best Practices Document

[Hooverdan96]

Fixes #444. Changes to be committed: modified: pre-install-howto.rst

• Updated memory testing section
• corrected minor typos
• harmonized title case across page to be in line with rest of documentation

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]

Only error occurs during link check for a known broken link, not related to the above changes.

(       data_loss: 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

This piece can now be found here: https://btrfs.readthedocs.io/en/latest/Glossary.html, however the whole paragraph in the Data Loss section needs to probably be updated, since a link to the sysadminguide also points to the now obsolete wiki also.

Linkcheck failure fixed with #447.

[phillxnet]

@Hooverdan96 Thanks for this most welcome improvement. And for your continued efforts in this direction. Much appreciated.

I'll merge now and publish once I've reviewed your other pending doc pull requests.

[phillxnet]

PR product PRODUCTION published.