readthedocs action on master

[hareball90]

when pushing to master branch, update the documentation so that a push/release on master triggers an update to readthedocs which updates pygom version release info and the link to the jupyterbook hosted on ghpages

[hareball90]

something like this https://readthedocs.org/projects/jupyter-book/

[hareball90]

use this example from jupyterbook tutorial deployment
https://github.com/executablebooks/jupyter-book/blob/master/.readthedocs.yml

[hareball90]

@twomagpi will need to give access to Joe / Steven for updating this

[hareball90]

Context
Originally the doc build was too large for RTD to compile. Fix: build a subset of docs on RTD and full docs locally.
Now, build the full documentation with github actions/pages, which will lnot be restricted to the same timeout constraint. Then if possible, upload htmls from the github build to readthedocs.

[twomagpi]

Need to either update / remove / massively simplfy the RTD pages following #114