Eleventy: Add contributing guidelines

[ogdenstudios]

Is your feature request related to a problem? Please describe.
Similar to #387, but perhaps with a wider scope. I know the technical details of how to patch Eleventy, make PRs, and otherwise contribute. But I don't know the preferred process for this community. I don't know what is an appropriate issue for me to look at, how to raise my hand to solve it, etc. etc.

Describe the solution you'd like
I'd love a contributing.md document added to the project. I love the Rails contribution guidelines, or the Mozilla guide. I imagine we don't need anything nearly as comprehensive, but those are guides I've always admired.

Describe alternatives you've considered
Doesn't need to be as formal as I've outlined, but perhaps even just something in the README about how you prefer to receive contributions. Or if you even want them.

[Ryuno-Ki]

In this vein, adding labels like „good first issue” could raise your visibility on GitHub. Other services are looking for something up for grabs.

Hacktoberfest showed some links for beginners to discover those types of issues.

[bikingbadger]

I'm trying to look at getting 11ty up and running for development to try and understand the code base and try help out with test examples that get asked in the issues. I'd also really appreciate any help getting it up and running.
So far I have cloned the repo and run npm link ../eleventy in my test project folder.
When I run 11ty in a test project I get it to actually run the cloned 11ty repo. My question now is how would i debug this code? In other words add a debugger.

[DirtyF]

See https://www.11ty.io/docs/debugging/

[bikingbadger]

Hi Frank,
That would help when throwing out debugging messages. If I want to actually step through the code during build time, how would I do that?
If you want to create a PR and check and test the code by stepping through it, how is this done?
Thanks