Add Versioning Policy to README (#167)

With the OTel Profiling signal v1experimental was introduced. This might break backwards compatability if v1experimental gets  replaced with v1.
Add a section to the Readme to make users aware of this risk.

README.md

@@ -4,6 +4,13 @@
 
 Generated Go code for the OpenTelemetry protobuf data model.
 
+## Versioning Policy
+
+The autogenerated Go code follows the stability guarantees as defined in
+[maturity
+level](https://github.com/open-telemetry/opentelemetry-proto?tab=readme-ov-file#maturity-level).
+Packages suffixed as `experimental` might not be kept indefinitely.
+
 ## Getting Started
 
 Install the latest version in your project.