[editorial] Add missing README.md for Resource Cloud Provider semco…

…nv (open-telemetry#171)

Co-authored-by: Joao Grassi <joao@joaograssi.com>
Co-authored-by: Armin Ruech <armin.ruech@dynatrace.com>

docs/resource/cloud_provider/README.md

@@ -0,0 +1,15 @@
+<!--- Hugo front matter used to generate the website version of this page:
+linkTitle: Cloud Provider
+--->
+
+# Resource Cloud Provider Semantic Conventions
+
+**Status**: [Experimental][DocumentStatus]
+
+This document defines semantic conventions for resource cloud providers.
+
+* [AWS](aws/README.md): Semantic Conventions for Amazon Web Services.
+* [GCP](gcp/README.md): Semantic Conventions for Google Cloud Platform.
+* [Heroku](heroku.md): Semantic Conventions for Heroku.
+
+[DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/blob/v1.21.0/specification/document-status.md