Add httpx-ws to third party packages. (#3325)

Co-authored-by: Tom Christie <tom@tomchristie.com>

Author: T-256

docs/third_party_packages.md

@@ -4,7 +4,11 @@ As HTTPX usage grows, there is an expanding community of developers building too
 
 ## Plugins
 
-<!-- NOTE: this list is in alphabetical order. -->
+### httpx-ws
+
+[GitHub](https://github.com/frankie567/httpx-ws) - [Documentation](https://frankie567.github.io/httpx-ws/)
+
+WebSocket support for HTTPX.
 
 ### httpx-socks