Add "CircuitPython" library issues and pull requests onto CircuitPython.org/contributing

There is a plan to add community-developed libraries into the [Github CircuitPython organization](https://github.com/circuitpython).

Currently, the [CircuitPython.org/contributing](https://circuitpython.org/contributing) pages includes open issues and open pull requests associated with the Adafruit libraries.

I suggest adding the new CircuitPython GitHub organization library issues and open Pull Requests into this page. This will provide one-place where contributors can go to easily see all the CircuitPython library-related PRs and open issues.

(@kattni mentioned that if this gets too overwhelming we could always break the different organizations into separate pages or tabs. For now, I think it's probably fine to just combine them all into one and see how it goes.)

Start by inspecting the CircuitPython.org/contributing page and the existing display of open Adafruit library issues and pull requests. Determine how those items are gathered, then confirm that open issues and pull requests from the CircuitPython GitHub organization libraries appear alongside them on the page.

Written by the indexing model from the issue text.