add/link out to instructions to deploy HTML built with Sphinx

[tobyhodges]

From feedback received during the pilot lesson at CC@Home2020: the lesson could be improved by adding, or linking out to instructions for deploying HTML files built with Sphinx. It was suggested that readthedocs could be a good choice for this.

[brownsarahm]

Is using only travis or gh-pages easier? I've only deployed docs with travis, so insight from others on what is the most feasible for actually getting to try it during the workshop would help.

I think that for the purposes of sharing, an "add this file and customize" might be easier than something with a lot of clicking through a gui interface to demonstrate and follow.

Also, need to consider, adding either in this episode or earlier an exercise to put whatever the "working" project is on github if it's not already (eg if learners are using an actual repo of theirs it might already be, if working with a toy it won't be (see: #1)