Update contributing docs to save people's time

[ahmed-hritani]

Result of #269.

Save people's time by defining the contributing constraints.

[iambumblehead]

It is good to expect some discussion when submitting changes to the README of a project.

[ahmed-hritani]

It is good to expect some discussion when submitting changes to the README of a project.

That's for sure, thing is that it's usually the case that such things are in the CONTRIBUTING.md file and such discussion happen before the PR is merged.

Thanks for the effort.

[iambumblehead]

That's true and also we're human and make mistakes.

[iambumblehead]

Two things that would reduce friction for README PRs imo,

1. README examples should also exist in live unit-tests verified by the testing job. This would enforce passing README tests and also increase the size of those PRs, increasing expectation of discussion,
2. The README linting should be fixed, so that the README is linted as part of the CI pipeline for each PR

[iambumblehead]

related eslint/markdown#227