Recipe documentation

[mattwthompson]

Describe the behavior you would like added to mBuild
I need to ask somebody to migrate a small repo into an mBuild recipe and the best documentation (barring me explaining it myself) is buried in a PR: #501 (comment)

Describe the solution you'd like
More thorough documentation, and probably an example of its use (i.e. https://github.com/ftiet/droplet-builder/blob/27fecdd81d060f8c51b0c3fb8bd06c4f6c2c15c9/setup.py#L48). A cookiecutter would be great too.

[rmatsum836]

Since work on mBuild recipes is starting to ramp up, I'm going to take a stab at creating a cookie cutter for these.

[mikemhenry]

Good idea! I've noticed that github now lets you mark repos when they are meant for being a template.

[CalCraven]

I believe the cookie cutter repo was created and works great by @rmatsum836. I think we need further documentation in order to point users to this, potentially in the README and on our website.