Update FRS terminology

Replace "FRS" with "AFR" and define acronym

Author: Josmithr

articles/azure-fluid-relay/how-tos/fluid-json-web-token.md

@@ -37,7 +37,7 @@ Each part is separated by a period (.) and separately Base64 encoded.
 
 | Claim      | Format                   | Description |
 |------------|--------------------------|-------------|
-| documentId | string                   | Generated by FRS, identifies the document for which the token is being generated. |
+| documentId | string                   | Generated by Azure Fluid Relay (AFR) service. Identifies the document for which the token is being generated. |
 | scope      | string[]                 | Identifies the permissions required by the client on the document or summary. For every scope, you can define the permissions you want to give to the client.  |
 | tenantId   | string                   | Identifies the tenant. |
 | user       | JSON                     | *Optional* `{ displayName: <display_name>, id: <user_id>, name: <user_name>, }` Identifies users of your application. This is sent back to your application by Alfred, the ordering service.  It can be used by your application to identify your users from the response it gets from Alfred. Azure Fluid Relay doesn't validate this information. |