merge duplicate "Getting Started" sections in doc

[dlyongemallo]

Following up on issue #59, there are now two sections called "Getting Started" in the doc, once from gettingstarted.rst and once from notebooks/gettingstarted.ipynb.

If there are no objections, I think any non-redundant info from the RST file can be moved into the Python notebook, and then the RST file can just be replaced by the Python notebook entirely.

For consistency, and maybe to add more interactivity, the other sections can also be migrated.

[jvdwetering]

That sounds like a good idea.