add organization profile/README.md

[dcamron]

See Unidata's organization profile for an example and documentation here. I'm glad to draft this in a week or two if we'd like something like this. Provides an overview of the project on our organization page.

[brian-rose]

Just attempting to re-up this! It would be great to get something simple put together that at a minimum just provides easy links to the portal as well as the other Pythia-related GitHub organizations (https://github.com/ProjectPythiaCookbooks, https://github.com/ProjectPythiaTutorials, ... ?)

[brian-rose]

This would also be one place to address the communication barrier issues described in ProjectPythia/projectpythia.github.io#267 and ProjectPythia/projectpythia.github.io#260