DOC: explain how to make a fixed-size axes

[jklymak]

PR Summary

Also added some facecolor to some of the figures that could use it.

PR Checklist

Documentation and Tests

• Has pytest style unit tests (and pytest passes)
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

[jklymak]

https://output.circle-artifacts.com/output/job/ddc569b7-fef5-4ed9-95e4-66d282c8502a/artifacts/0/doc/build/html/tutorials/intermediate/arranging_axes.html#adding-single-axes-at-a-time

[rcomer]

Huh. I didn’t know you could pass a position into add_subplot, and would have expected this example to use add_axes. Even now I know, the docstring is confusing: pos is listed in the valid call signatures, but not described under parameters.

So is add_axes redundant api or is there some difference in what you would get?

[jklymak]

Switched to add_axes. I actually meant to do that originally.

I don't understand why CI is running. I thought the Actions check would work here...

[jklymak]

@rcomer is this OK now?