Add Contributor Setup Documentation

[ccjernigan]

Is your feature request related to a problem? Please describe.

We have a number of ECC team members who are not familiar with IntelliJ and Kotlin. To help them be able to build this project from source, we should have easy to follow setup instructions.

Describe the solution you'd like

Something similar to https://github.com/zcash/secant-android-wallet/blob/main/docs/Setup.md