Encodings: Add readme. (#245)

Author: songy23

encodings/BinaryEncoding.md

@@ -144,7 +144,3 @@ https://developers.google.com/protocol-buffers/docs/encoding#varints.
   example, a serialized tag context with 10,000 small tags that all have the
   same key should be considered too large.
 
-## Related Work
-* [TraceContext Project](https://github.com/TraceContext/tracecontext-spec)
-* [Stackdriver TraceContext Header](https://cloud.google.com/trace/docs/support)
-* [B3 TraceContext Header](https://github.com/openzipkin/b3-propagation)

encodings/README.md

@@ -0,0 +1,15 @@
+# OpenCensus Library Encoding Package
+This documentation serves to document the on-the-wire encoding format supported in
+OpenCensus. It describes the key types and the overall behavior.
+
+## Formats
+* [Binary Encoding](BinaryEncoding.md)
+  * [TraceContext Binary Encoding](BinaryEncoding.md#trace-context)
+  * [TagContext Binary Encoding](BinaryEncoding.md#tag-context)
+  * [Census Server Stats Encoding](CensusServerStatsEncoding.md)
+
+* HTTP Encoding
+  * [W3C TraceContext](https://github.com/TraceContext/tracecontext-spec)
+  * [W3C Correlation Context](https://github.com/w3c/correlation-context)
+  * [Stackdriver TraceContext Header](https://cloud.google.com/trace/docs/support)
+  * [B3 TraceContext Header](https://github.com/openzipkin/b3-propagation)