pip install instructions

Also a better ReadMe.

PR Checklist

[ ] Give a detailed description of the PR above.
[ ] Document changes in the CHANGES.rst file. See existing changelog for examples.
[ ] Add tests, if applicable, to ensure code coverage never decreases.
[ ] Make sure the docs are up to date, if applicable, particularly the docstrings and RST files in docs folder.
[ ] Ensure linear history by rebasing, when requested by the maintainer.