docs: improving websocket docs (#8156)

Making it clear H2 websockets don't work by default

Risk Level: n/a
Testing: n/a
Docs Changes: yes
Release Notes: no
#8147

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

docs/root/intro/arch_overview/http/websocket.rst

@@ -36,19 +36,21 @@ Note that the statistics for upgrades are all bundled together so WebSocket
 :ref:`statistics <config_http_conn_man_stats>` are tracked by stats such as
 downstream_cx_upgrades_total and downstream_cx_upgrades_active
 
-Handling H2 hops
-^^^^^^^^^^^^^^^^
+Handling HTTP/2 hops
+^^^^^^^^^^^^^^^^^^^^
 
-Envoy supports tunneling WebSockets over H2 streams for deployments that prefer a uniform
-H2 mesh throughout; this enables, for example, a deployment of the form:
+While HTTP/2 support for WebSockets is off by default, Envoy does support tunneling WebSockets over
+HTTP/2 streams for deployments that prefer a uniform HTTP/2 mesh throughout; this enables, for example,
+a deployment of the form:
 
 [Client] ---- HTTP/1.1 ---- [Front Envoy] ---- HTTP/2 ---- [Sidecar Envoy ---- H1  ---- App]
 
 In this case, if a client is for example using WebSocket, we want the Websocket to arrive at the
 upstream server functionally intact, which means it needs to traverse the HTTP/2 hop.
 
-This is accomplished via
-`extended CONNECT <https://tools.ietf.org/html/rfc8441>`_ support. The
+This is accomplished via `extended CONNECT <https://tools.ietf.org/html/rfc8441>`_ support,
+turned on by setting :ref:`allow_connect <envoy_api_field_core.Http2ProtocolOptions.allow_connect>`
+true at the second layer Envoy. The
 WebSocket request will be transformed into an HTTP/2 CONNECT stream, with :protocol header
 indicating the original upgrade, traverse the HTTP/2 hop, and be downgraded back into an HTTP/1
 WebSocket Upgrade. This same Upgrade-CONNECT-Upgrade transformation will be performed on any
@@ -57,5 +59,5 @@ Non-WebSocket upgrades are allowed to use any valid HTTP method (i.e. POST) and
 upgrade/downgrade mechanism will drop the original method and transform the Upgrade request to
 a GET method on the final Envoy-Upstream hop.
 
-Note that the H2 upgrade path has very strict HTTP/1.1 compliance, so will not proxy WebSocket
+Note that the HTTP/2 upgrade path has very strict HTTP/1.1 compliance, so will not proxy WebSocket
 upgrade requests or responses with bodies.