Add initial AI agent guide

[djhoese]

Written by Claude. Reviewed by me. Claude identified some possibly major issues so I'd like to get it working on those.

• Closes #xxxx
• Tests added
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff
• Fully documented

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.04%. Comparing base (3ccdf6f) to head (e74a0ef).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   88.75%   89.04%   +0.28%     
==========================================
  Files          20       20              
  Lines        1521     1515       -6     
==========================================
- Hits         1350     1349       -1     
+ Misses        171      166       -5     

Flag	Coverage Δ
unittests	89.04% <ø> (+0.28%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[pnuu]

LGTM

[coveralls]

coverage: 88.176%. remained the same — djhoese:feat-agent-guide into pytroll:main

[djhoese]

Given the size and audience of this library I'm going to merge this and deal with problems with it later. I'd like to start working on some of these bugs.