Add.fre.pp.readme

[ilaflott]

Describe your changes

Issue ticket number and link (if applicable)

Checklist before requesting a review

• I ran my code
• I tried to make my code readable
• I tried to comment my code
• I wrote a new test, if applicable
• I wrote new instructions/documentation, if applicable
• I ran pytest and inspected it's output
• I ran pylint and attempted to implement some of it's feedback

[ceblanton]

When we merge this in, we expect the github io docs here to update right?

https://noaa-gfdl.github.io/fre-cli/index.html

Let's give it a test!

[ceblanton]

Thanks Ian! I owe the documentation a bunch more and this is a great test of the process.