Update README with more context and links (#99)

[ci skip]

Author: rgommers

README.md

@@ -1,7 +1,27 @@
 # Dataframe API standard
 
 This repository contains documents, tooling and other content related to the
-API standard for dataframes.
+API standard for dataframes, and the dataframe interchange protocol.
+
+
+## Dataframe API standard (draft)
+
+This API is _draft and under development_, and moving towards an RFC status
+where wider input from authors of dataframe and dataframe-consuming libraries
+will be solicited. Those authors are the primary audience for this API, rather
+than end users. Relevant content and links:
+
+- [Dataframe API standard documentation](https://data-apis.org/dataframe-api/draft/index.html)
+
+
+## Dataframe interchange protocol
+
+This protocol is released and the specification should be considered stable. It
+has implementations in multiple dataframe libraries (Pandas, cuDF, Modin, Vaex
+at least). It may be extended and receive other necessary tweaks for things
+discovered in the process of being adopted by a wider set of libraries.
+Relevant content and links:
 
-- [Request For Comments (RFC) for the dataframe interchange protocol (blog post)](https://data-apis.org/blog/dataframe_protocol_rfc/)
 - [Dataframe interchange protocol documentation](https://data-apis.org/dataframe-protocol/latest/index.html)
+- Issue tracker: [`interchange-protocol` label in this repo](https://github.com/data-apis/dataframe-api/issues?q=is%3Aopen+is%3Aissue+label%3Ainterchange-protocol)
+- [Request For Comments (RFC) for the dataframe interchange protocol (blog post)](https://data-apis.org/blog/dataframe_protocol_rfc/)