Update README.md

Changes to README.md:

* Removed Fly.io logo, which does make it look like we think it's official.
* Added a bolded line at the top to indicate that this is not a recommended way to deploy to Fly.io and isn't maintained.

README.md

@@ -1,9 +1,9 @@
-![Fly.io logo](/imgs/fly.png)
-
 # fly.io terraform provider
 
 [![Tests](https://github.com/fly-apps/terraform-provider-fly/actions/workflows/test.yml/badge.svg)](https://github.com/fly-apps/terraform-provider-fly/actions/workflows/test.yml)
 
+**This is not an officially supported or maintained project and is not a recommended method of deployment to Fly.io.**
+
 ### Resources
 - app (stable, but apps will be deprecated soon. Begin to favor machines.)
 - cert (stable)