Supported React versions should be documented on the web site.

[dlabaj]

trafficstars

Currently the supported versions of React that work with PatternFly are missing from the website. We should add to the site the versions we currently support for react. It can most likely be added in this section (https://www.patternfly.org/get-started/develop#develop-with-react), along with a statement saying we support 2 major versions at a time.