* Added a how-to on react-snapshot

Added a section with a short description and link to a tutorial on generating static html pages with react-snapshot, and also linked to it from the section on managing the page title.

* Updated link title for react-snapshot overview

* Explained pre-rendering in a more generic way

* Added link to top level README.md, and removed specifics from overview

* Updated html -> HTML

* Updated quotes and apostrophes

* html -> HTML

* Fix link