update docs

docs/content/1.get-started/3.tips/3.authorization.md

@@ -6,6 +6,10 @@ title: Authorization
 
 The `createContext` function is called for each incoming request so here you can add contextual information about the calling user from the request object.
 
+::alert{type="info"}
+Before you can access request headers in any context or middleware, you need to set the outgoing request headers. See [here](/get-started/tips/headers).
+::
+
 ## Create context from request headers
 
 ```ts [server/trpc/context.ts]