Remove outdated information in intro section of documentation

Fixes #1337

docs/intro.rst

@@ -101,9 +101,8 @@ Client Features
 ---------------
 
 - Can connect to other Socket.IO servers that are compatible with the
-  JavaScript Socket.IO 1.x and 2.x releases. Work to support release 3.x is in
+  JavaScript Socket.IO reference server.
-  progress.
+- Compatible with Python 3.8+.
-- Compatible with Python 3.6+.
 - Two versions of the client, one for standard Python and another for
   asyncio.
 - Uses an event-based architecture implemented with decorators that
@@ -181,9 +180,8 @@ Server Features
 ---------------
 
 - Can connect to servers running other Socket.IO clients that are compatible
-  with the JavaScript client versions 1.x and 2.x. Work to support the 3.x
+  with the JavaScript reference client.
-  release is in progress.
+- Compatible with Python 3.8+.
-- Compatible with Python 3.6+.
 - Two versions of the server, one for standard Python and another for
   asyncio.
 - Supports large number of clients even on modest hardware due to being
@@ -195,8 +193,8 @@ Server Features
 - Can be integrated with WSGI applications written in frameworks such as Flask, Django,
   etc.
 - Can be integrated with `aiohttp <http://aiohttp.readthedocs.io/>`_,
-  `sanic <http://sanic.readthedocs.io/>`_ and `tornado <http://www.tornadoweb.org/>`_
+  `FastAPI <https://fastapi.tiangolo.com/>`_, `sanic <http://sanic.readthedocs.io/>`_
-  ``asyncio`` applications.
+  and `tornado <http://www.tornadoweb.org/>`_ ``asyncio`` applications.
 - Broadcasting of messages to all connected clients, or to subsets of them
   assigned to "rooms".
 - Optional support for multiple servers, connected through a messaging queue