Mention #synapse:matrix.org in README troubleshooting (#7603)

Just in case people head straight to the troubleshooting section and find themselves at a dead end.

README.rst

@@ -267,7 +267,7 @@ First calculate the hash of the new password::
     Confirm password:
     $2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 
-Then update the `users` table in the database::
+Then update the ``users`` table in the database::
 
     UPDATE users SET password_hash='$2a$12$xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
         WHERE name='@test:test.com';
@@ -335,6 +335,9 @@ Building internal API documentation::
 Troubleshooting
 ===============
 
+Need help? Join our community support room on Matrix:
+`#synapse:matrix.org <https://matrix.to/#/#synapse:matrix.org>`_
+
 Running out of File Handles
 ---------------------------
 

changelog.d/7603.doc

@@ -0,0 +1 @@
+Add a link to `#synapse:matrix.org` in the troubleshooting section of the README.