Add README

[npotier]

Hello,

First of all, thank you for this project.

I think it would be a good idea to add a README to the project, and to give information on how to use it to test a contrib recipe locally before asking for a merge on the contrib repository on Github.

I discovered the recipes-checker following a conversation on Stack Overflow here : https://stackoverflow.com/a/71761865

I you think its a good idea I could try to write it.