Add installation instructions

[jklaise]

This PR adds the missing installation instructions. This is particularly needed because the PyPI package name is mlops-tempo as tempo is taken and is a completely different package.

FYI when building the docs, the two .rst files under docs/api were flagged as changed, so I've included them into this PR. Let me know if these changes are expected and/or if these need to be split out into a different PR.