VAPI-1526 added uui property, description and example (#1098)

* VAPI-1526 added uui property, description and example

* indentation is done

* Indentation changes

Author: atelegu

site/docs/voice/webhooks/initiate.mdx

@@ -27,6 +27,7 @@ The Initiate event is fired when an inbound call is received for a Telephone Num
 | applicationId     | The id of the application associated with the call. |
 | to                | The phone number that received the call, in E.164 format (e.g. +15555555555). |
 | from              | The provided identifier string of the caller used in the `from` field of the original call. |
+| uui               | (optional) The value of the `User-To-User` header to send within the initial `INVITE`. Must include the `encoding` parameter as specified in [`RFC 7433`](https://tools.ietf.org/html/rfc7433). Only `base64` and `jwt` encoding are currently allowed. This value, including the encoding specifier, may not exceed 256 characters. |
 | direction         | The direction of the call; can only be `inbound`. The direction never changes. |
 | callId            | The call id associated with the event. |
 | callUrl           | The URL of the call associated with the event. |
@@ -91,3 +92,26 @@ Content-Type: application/json
 	}
 }
 ```
+
+### Initiate Event with uui Information
+
+```json
+POST http://yourUrl.example/initiate
+Content-Type: application/json
+
+{
+	"eventType"     : "initiate",
+	"eventTime"     : "2019-06-20T15:56:11.554Z",
+	"accountId"     : "55555555",
+	"applicationId" : "7fc9698a-b04a-468b-9e8f-91238c0d0086",
+	"from"          : "+15551112222",
+	"to"            : "+15553334444",
+    "uui"           : "eyJhbGciOiJIUzI1NiJ9.WyJoaSJd.-znkjYyCkgz4djmHUPSXl9YrJ6Nix_XvmlwKGFh5ERM;encoding=jwt,aGVsbG8gd29ybGQ;encoding=base64",
+	"direction"     : "inbound",
+	"callId"        : "c-95ac8d6e-1a31c52e-b38f-4198-93c1-51633ec68f8d",
+	"callUrl"       : "https://voice.bandwidth.com/api/v2/accounts/55555555/calls/c-95ac8d6e-1a31c52e-b38f-4198-93c1-51633ec68f8d",
+	"startTime"     : "2019-06-20T15:54:22.234Z"
+}
+```
+
+