Organize badges, define supported Python versions, and update versioneer

[BrianJKoopman]

Description

This PR cleans up a few things:

• Organizes and adds to the badges in the README.
• Adds an explicit list of supported Python versions to the classifiers list. This'll show up in one of the new badges, as well as the side bar on PyPI.
• Updates versioneer to the latest version, 0.29.

Motivation and Context

Mostly uniformity with other repos like socs and sorunlib. See simonsobs/socs#673.

How Has This Been Tested?

Tested the versioneer update locally, and the README changes viewing this branch on GitHub.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.