Add CONTRIBUTING.md document

[dswarbrick]

Initial cut of CONTRIBUTING document, containing basic guidelines for textfile collector scripts in this repo.

@SuperQ Can you think of anything we need to add / remove?

[lstrojny]

How should Python scripts state requirements beyond prometheus-client?

[SuperQ]

One idea, we could move to having directory-per-script and requirements.txt files for python scripts.

[lstrojny]

Yup, that's certainly possible. I am a Python noob, especially on tooling, so is there a way to do pip install github.com:org/repo/subfolder#revision or something similar?

[anarcat]

not really. you can pip install . from within a directory, but typically you'd ship this whole project as one big project on pypi and install it as one chunk.

that said, i am not sure you'd want to set that as policy right now. i would suggest you start with the drafted policy as is, and then maybe iterate once this PR is merged, as python packaging is rather more complicated than, say, shell scripts.

personnally, i wouldn't do the requirements.txt dance at all and keep things at a simple one-file-per-script approach. more complicated exporters should just have their own git projects IMHO.

[dswarbrick]

Like @anarcat, I think that once something crosses the threshold of being pip-installable, it really ought to move to its own repo which can better cater to its needs such as having a requirements.txt, and the main focus of that repo being $foo.

If we were going to make this repo pip-installable, I think we would need to more accurately define what the mission of this repo is. At present, it's just a jumble of unrelated textfile collector scripts, which is fine - so long as it doesn't promise to be anything more.