Clarify an example that does not work as it is [ci-skip]

This snippet was hard to decipher and I'd like to propose that it be clarified.

`'_your_app_session'` as the default name of the cookie is a common placeholder
throughout the guides which we can use for consistency.

With these changes we are less likely to cause an immediate trouble,
which is the NoMethodError as a result of `cookie.encrypted['_session']` being nil.

guides/source/action_cable_overview.md

@@ -131,12 +131,10 @@ by this same current user, you're also ensuring that you can later retrieve all
 connections by a given user (and potentially disconnect them all if the user is deleted
 or unauthorized).
 
-If your authentication approach includes using a session, you use cookie store for the
-session, your session cookie is named `_session` and the user ID key is `user_id` you
-can use this approach:
+If your authentication approach includes using a session, you can use this approach:
 
 ```ruby
-verified_user = User.find_by(id: cookies.encrypted['_session']['user_id'])
+verified_user = User.find_by(id: cookies.encrypted['_your_app_session']['user_id'])
 ```
 
 [`ActionCable::Connection::Base`]: https://api.rubyonrails.org/classes/ActionCable/Connection/Base.html