Chore: Add Facebook app set up documentation (#647)

Co-authored-by: Pranav Raj S <pranavrajs@gmail.com>

app/javascript/dashboard/api/channel/fbChannel.js

@@ -3,7 +3,7 @@ import ApiClient from '../ApiClient';
 
 class FBChannel extends ApiClient {
   constructor() {
-    super('facebook_indicators');
+    super('facebook_indicators', { accountScoped: true });
   }
 
   markSeen({ inboxId, contactId }) {
@@ -22,7 +22,7 @@ class FBChannel extends ApiClient {
 
   create(params) {
     return axios.post(
-      `${this.apiVersion}/callbacks/register_facebook_page`,
+      `${this.url.replace(this.resource, '')}callbacks/register_facebook_page`,
       params
     );
   }