add installation / usage instructions to readme

[donovanr]

• brightfield2fish version:
• Python version:
• Operating System:

Description

Describe what you were trying to get done. Tell us what happened, what went wrong, and what you expected to happen.

What I Did

Paste the command(s) you ran and the output.
If there was a crash, please include the traceback here.

[donovanr]

closed with 6fb40de14a8c6af1b3cf314f5bacb7496d0726b4