More developer & maintainer sections for CONTRIBUTING

[karalekas]

Brain dump of some things that came to mind recently:

• developer section about latex module
• ~~maintainer section about .gitlab-ci.yml and Makefile~~ https://github.com/rigetti/pyquil/pull/1166
• maintainer section about top-level text documents (ack, license, notice)
• developer section about setting up python + Forest dev environment
• maintainer section about the external module (subsume readme)
• ~~maintainer section about producing the conda-forge package~~ https://github.com/rigetti/pyquil/pull/1186
• pull the parser readme stuff into the contributing guide
• pull whatever else is in the docs readme into the guide
• maintainer section about PR approvals, teams, and codeowners
• ~~developer section about using / adding to the examples~~ https://github.com/rigetti/pyquil/pull/1167 https://github.com/rigetti/forest-tutorials#contributing-your-own-tutorial-notebook
• ~~add mypy stuff to the style section once it is done~~ https://github.com/rigetti/pyquil/pull/1157

[karalekas]

also add a checkbox to the PR template when the parser one is done