Fix 32-bit libgpiod_pulsein and Doc updates

What's Changed

• Compiled libgpiod_pulsein with static linking to fix missing library #1032 by @makermelissa
• docs: add python3-dev to build.apt_packages in RTD config #1028 by @2bndy5
• docs: update build CI status badge in README #1029 by @2bndy5

To use in CPython, pip3 install adafruit-blinka.

Read the docs for info on how to use it.