Chore: Add docs for Twilio Whatsapp/SMS channel (#804)

docs/channels/whatsapp-sms-twilio.md

@@ -0,0 +1,51 @@
+---
+path: "/docs/channels/whatsapp-sms-twilio"
+title: "How to create a Whatsapp/SMS channel with Twilio?"
+---
+
+**Step 1**. Click on "Add Inbox" button from Settings > Inboxes page.
+
+![sms_create](./images/twilio/inbox_create.png)
+
+**Step 2**. Click on "Twilio" icon.
+
+![list_of_channels](./images/twilio/list_of_channels.png)
+
+**Step 3**. Configure the inbox.
+
+These are input required to create this channel
+
+| Input | Description | Where can I find it |
+| -- | -- | -- |
+| Channel Name | This is the name inbox, this will used across the application | N/A |
+| Channel Type | Select SMS if you are integrating SMS channel, select Whatsapp if you have a verified Whatsapp number in Twilio | N/A |
+| Phone Number | This is number you will be using to communicate with you customer, this has to be verified in Twilio | Enter your number as in Twilio Dashboard  |
+| Account SID | Account SID in Twilio Console | Login to Twilio Console, you would be able to see Account SID and Auth Token |
+| Auth Token | Auth token for the account | Login to Twilio Console, you would be able to see Account SID and Auth Token |
+
+![create_twilio](./images/twilio/create_twilio_inbox.png)
+
+**Step 4**. "Add agents" to your inbox.
+
+![add_agents](./images/add_agents.png)
+
+**Step 6**. Hooray! You have sucessfully created a whatsapp/sms inbox.
+
+![finish_inbox](./images/twilio/finish_inbox.png)
+
+If it is an SMS Channel then you don't need to do anything else, you will start receiving the messages in the dashboard whenever a customer sends you one.
+
+If you are connecting a **Whatsapp** channel, you have configure a callback URL in the Twilio inbox.
+
+- Login to your Twilio Console.
+- Go to `Programmable SMS > Whatsapp > Senders`
+- You will be able to see your phone number. Click on it, it will display a field like the one below.
+
+![twilio_console](./images/twilio/twilio_console.png)
+
+- Provide `https://app.chatwoot.com/twilio/callback` as the value for `WHEN A MESSAGE COMES IN` input.
+
+
+**Step 7**. If you want to update the agents who have access to the inbox, you can go to Settings > Inboxes.
+
+![inbox_settings](./images/twilio/inbox_settings.png)