[README] Add link to KSP plugin

[VWoeltjen]

Add link to David Hudson's Kerbal Space Program plugin from #1146,
along with other information about Examples relevant in that context.

Resolves #1064

Author Checklist

1. Changes address original issue? Y
2. Unit tests included and/or updated with changes? N/A (doc-only changes)
3. Command line build passes? Y
4. Changes have been smoke-tested? Y

[akhenry]

Reviewer Checklist

1. Changes appear to address issue? Y
2. Appropriate unit tests included? N/A - Documentation change only
3. Code style and in-line documentation are appropriate? N/A
4. Commit messages meet standards? Y