Missing installation instructions

[speth]

I could not find any installation instructions. While I found that running the common pip install -e . from a Git checkout worked, even this installation route should be documented.

• There is nothing mentioned in README.md
• There is no separate INSTALL.md
• There is no information available via the linked documentation website (https://uw-comphys.github.io/openccm/)
• There is no "release" version marked on GitHub, and the only tagged version is v0.9. Meanwhile, the version available from PyPI is v0.1.
• The method for installing with the extra dependencies for the examples should be documented. I had to read setup.cfg and search Stack Overflow to learn that the correct command is pip install -e ".[all]" .

This is in the context of the review for JOSS (https://github.com/openjournals/joss-reviews/issues/6963).

[Alex-Vasile]

Hi @speth, I am going to break out the release problem into it's own issue as it's not documentation related