Update README with more installation options

[PeterDSteinberg]

Discuss:

• Installing from dev vs main package
• Installing from setup.py
• Git tagging and release system
• How packages are built and what their version pinning is like
• Do each of the above in the README for Tax-Calculator, webapp-public, B-Tax, OG-USA, and cross-link the README files as needed
• Revisit the new docs created under this issue after webapp PR 553 is merged (deploy repo refactor)

This issue is in response to discussion on #1368

[MattHJensen]

Thanks for opening this @PeterDSteinberg!

[martinholmer]

There has been no discussion of the points listed in issue #1370 since the issue was first raised three months ago. This suggests there is not much demand for the additional installation options listed in #1370. So, this issue is being closed. If developers would like any of these extra features, they can raise a new issue describing what the desired new installation option is and why it would be helpful in their workflow.