Create core distribution component criteria (open-telemetry#500)

distributions/otelcol/README.md

@@ -1,7 +1,14 @@
-# OpenTelemetry Collector Distro
+# OpenTelemetry Collector Core Distro
 
-This distribution contains all the components from the [OpenTelemetry Collector](https://github.com/open-telemetry/opentelemetry-collector) repository and a small selection of  components tied to open source projects from the [OpenTelemetry Collector Contrib](https://github.com/open-telemetry/opentelemetry-collector-contrib) repository.
+This distribution contains all the components from the [OpenTelemetry Collector](https://github.com/open-telemetry/opentelemetry-collector) repository and a small selection of components tied to open source projects from the [OpenTelemetry Collector Contrib](https://github.com/open-telemetry/opentelemetry-collector-contrib) repository.
+
+This distribution is considered "classic" and is no longer accepting new components outside of components from the Core repo.
 
 ## Components
 
 The full list of components is available in the [manifest](manifest.yaml)
+
+### Rules for Component Inclusion
+
+Since Core is a "classic" distribution its components are strictly limited to what currently exists in its [manifest](manifest.yaml) and any future components in Core.
+No other components from Contrib should be added.