[Docs] Tap-Hold examples

[DesyncTheThird]

Description

Added some tap-hold examples, along with some slight reformatting:

• Minor punctuation changes;
• Added some tap-hold examples for filtering keys by tap-hold behaviour, and mod-tap keys by mods;
• Added a link about home row mods to the reference near the end;
• Replaced directional quotation marks with symmetric variant as this seem to be the only page using them;
• Standardised formatting of "tap-hold" (hyphenated is slightly more frequent in existing documentation, so I went with that), as well as "Mod-Tap"/"Layer-Tap".

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

I am struggling to get qmk docs working on my Windows machine (have troubleshooted this briefly on the QMK discord), so I have not been able to test these changes. I may have access to a Linux machine in a week's time (w.c. 16th), so I will try to test it then.