Update README before 1.x release

Problem/Motivation

The README file is out of date and needs accurate information.

Remaining tasks

It should clearly document some of the newer enhancements brought about by:

• #3192412: Improve block context definition and processing
• #3179739: Improve library definition to allow more complex definitions
• #3192674: Components discovery search dirs
• #3179730: Use a custom info parser method so that the info.yml files won't need keys required by modules