Simplify README, move content to documentation

[mdpiper]

This PR includes a pair of changes to the documentation:

1. With recent changes to the babelizer API (e.g., Remove options for babelize generate command #91 and Replace cookiecutter #96), information in README.rst was out of date.
2. Including the contents of README.rst in the docs made them harder to navigate (see Add link to docs in the About section and README #98 and Fix installation with Conda #99).

To address these changes, I updated the content in README.rst, but then moved most of that content to the docs, leaving a much simpler README with links to the documentation.

This fixes #98 and fixes #99.

[mcflugen]

@mdpiper How about significantly paring back the readme file and moving most everything to readthedocs? I've done something like that in bmi-wavewatch3 and I think it works pretty well.

[mdpiper]

@mcflugen Sounds good! I'll do this next.

[aufdenkampe]

Thanks for doing this! When I ran through the C Example (as described in #102), I was surprised that there was no mention of the move to using meson build system (#87, #90). It seems like it all happens under the hood. Regardless, is there any value in mentioning meson in these docs?