Update docs build to match pystac

[jsignell]

Related Issue(s): Closes #386

Description: Make the docs build more similar to pystac

PR checklist:

• [x] Code is formatted (run scripts/format).
• [x] Code lints properly (run scripts/lint).
• [x] Tests pass (run scripts/test).
• [x] Documentation has been updated to reflect changes, if applicable.
• [ ] Changes are added to the CHANGELOG. -> not needed I think

[jsignell]

Not sure how to test the readthedocs config changes.

[gadomski]

Not sure how to test the readthedocs config changes.

Looks like we get https://stactools--446.org.readthedocs.build/en/446/?