Tidy up code

[jklenzing]

Description

Updates the setup requirements following the examples of the other codes. Also updates readme and descriptions.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change is a documentation update

Checklist:

• Make sure you are merging into the develop (not master) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes

[jklenzing]

Added matplotlib back in since this will not be a requirement for pysat 3.0.0. Save us a few headaches in the future.

[rstoneback]

Looks good.