Update cloud-sql-proxy_wait.md

Without --health-check or --prometheus, the server http does not start

Author: sjeandeaux

docs/cmd/cloud-sql-proxy_wait.md

@@ -23,13 +23,14 @@ Configuration
 
   By default, the Proxy will wait up to the maximum time for the startup
   endpoint to respond. The wait command requires that the Proxy be started in
-  another process with the HTTP health check enabled. If an alternate health
+  another process with the HTTP health check or prometheus enabled. If an alternate health
   check port or address is used, as in:
 
   ./cloud-sql-proxy <INSTANCE_CONNECTION_NAME> \
     --http-address 0.0.0.0 \
     --http-port 9191
-
+    --health-check 
+  
   Then the wait command must also be told to use the same custom values:
 
   ./cloud-sql-proxy wait \