Create keystore documentation

[erinreeves]

Summary

As a	developer????
I want to be able to	understand keystores
So that I can	do development on security toggled features

• [ ] We need to identify what all should be in a keystore document and create it.

• [ ] Add a link to the doc in Feature Toggles section in here https://cedardevs.github.io/onestop/developer/additional-developer-info.md Update also where we say "More information to come"