Update keymap.c for dichotomy/alairock

[alairock]

Description

Add page up and down next to arrows,
Add command and shift to layer, which helps with ergonomics while on this layer. F keys overwritten are not common and will soon be move to a new layer entirely.

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

• Better layout for dichotomy/alairock

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).