Move open letter to the Airtime community to this repository

[jooola]

@hairmare Hey, I would like to move the open letter to the Airtime community into the LibreTime repository.

https://gist.github.com/hairmare/8c03b69c9accc90cfe31fd7e77c3b07d

Is that ok for you ?

It is causing a lot of HTTP 429 with our link checker, and was thinking about moving it under the libretime umbrella for some time now, as part of the history documents.

[paddatrapper]

Maybe under the organization repo?