Docs: Talks and Demos

[daveyarwood]

See #8 for context.

This should be done by modifying the docs folder in alda-lang/alda. The docs are kept in sync with releases and used to generate http://alda.readthedocs.io, which will be CNAMEd to docs.alda.io.

This section could include links like the ones I listed on my GitHub sponsors page.