Included additional steps for installing natlink

[DanKaplanSES]

Update docs

Description

This includes undocumented but required steps for installing natlink. This'll save me (and the next person) 30-60 minutes of effort the next time they install caster.

I also renamed the bullet points in the section to 1.. This makes it easy to rearrange, add, and delete bullet points without needing to re-number them all, but it renders in the correct order.

Related Issue

Motivation and Context

How Has This Been Tested

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue or bug)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Renamed existing command phrases (we discourage this without a strong rationale).

Checklist

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have checked that my code does not duplicate functionality elsewhere in Caster.
• My code implements all the features I wish to merge in this pull request.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests pass.

Maintainer/Reviewer Checklist

• Basic functionality has been tested and works as claimed.
• New documentation is clear and complete.
• Code is clear and readable.

[LexiconCode]

Thank you!