Update Changelog and README

[ojeda-e]

Before release 0.0.3 update changelog:

• [x] Add update on documentation to generate correct plots.
• [x] Improved performance with WarnOnce.

[ojeda-e]

Also update README and add brief sections on:

• [x] how to plot correct MC results.
• [x] encourage users to use last release instead of 0.0.2.