update docs

docs/content/1.get-started/3.tips/5.headers.md

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+---
+title: Headers
+---
+
+# Headers
+
+We can use the built-in `useRequestHeaders` to access/pass headers to any future internal requests during SSR.
+
+```ts [plugins/client.ts]
+import { httpBatchLink, createTRPCProxyClient } from '@trpc/client'
+import type { AppRouter } from '@/server/trpc/routers'
+
+export default defineNuxtPlugin(() => {
+  const headers = useRequestHeaders()
+
+  const client = createTRPCProxyClient<AppRouter>({
+    links: [
+      httpBatchLink({
+        headers() {
+          return {
+            ...unref(headers)
+          }
+        }
+      }),
+    ],
+  })
+
+  return {
+    provide: {
+      client,
+    },
+  }
+})
+```
+
+```ts [server/trpc/context.ts]
+export function createContext (event: H3Event) {
+  console.log('cookies', parseCookies(event))
+
+  return {}
+}
+```