chore: minor doc corrections and edits

[dav1do]

Description

As I was reading the docs, I corrected some out of date information, invalid links and made minor grammar edits.

How Has This Been Tested?

I previewed the markdown changes in the github branch and verified the links worked.

PR checklist

Before submitting this PR, please make sure:

• [x] I have tagged the relevant reviewers and interested parties
• [x] I have updated the READMEs of affected packages
• [x] I have made corresponding changes to the documentation

References:

n/a

[dav1do]

I suspect this is going to be immediately out of date with #3062 so I'm going to come back to it next week.