Clarify authentication for /twitch/subage

static/yaml/endpoints/twitch.yaml

@@ -201,6 +201,7 @@ endpoints:
           type: "int"
       notes:
         - "Returns the time since the subscription was started."
+        - '<strong>This only works for channels that have <a href="{{baseUrl}}/auth/twitch?scopes=user_read+channel_subscriptions+channel_check_subscription&redirect=subage" target="_blank" rel="noopener noreferrer">authenticated and authorized</a> this app</strong>, regardless if they already use subcount/subpoints.'
         - '<span class="text text-warning">Subscription age" in this case is a pretty loose term, as there is something called a subscription anniversary that is typically posted in chat (e.g. "Decicus has been subscribed for 21 months in a row!"). This is <strong>not the same</strong> as the anniversary.</span>'
         - '<span class="text text-warning">This endpoint only counts the time since the subscription payments started. So if someone changes their payment information, this will only count the time since they updated their payment information.</span>'
         - '<span class="text text-warning">Another good example is Twitch Prime subscriptions: If you have a user consistently subscribing to you with their Twitch Prime every month, this endpoint will reset every single month for that specific user.</span>'