LMW-85 Added requirements section
LMW-85 Add list of available widgets
LMW-85 Added auth widgets documentation pages
LMW-85 Changes from @juanferrub revision

https://github.com/liferay/liferay-screens/pull/46
Merge pull request #45 from liferay/LMW-85-documentation-for-widgets

LMW-85 documentation for widgets