Adding README.md for main repository

[Aksgo]

Hey @romain-fontugne,
To help any new user who wants to work on this project understand the underlying Kafka implementation, I would like to add a README.md file to the repository's main page. You can see a sample in my fork of your repository.
Please assign this task to me.
Thanks

[Aksgo]

Hello @romain-fontugne , can you please confirm if it is required or not?

[romain-fontugne]

Hi, thanks for your help, I don't think we need any explanations about Kafka here. We could just add links to the readmes in the subfolders but that's not really a priority