docs: add explanation about the auth in the optimizer (#7207)

Author: Kampouse

packages/docs/src/routes/docs/integrations/authjs/index.mdx

@@ -106,7 +106,16 @@ When migrating from `@builder.io/qwik-auth` to `@auth/qwik`, there are a couple
     +export const { onRequest, useSession, useSignIn, useSignOut } = 
     +  QwikAuth$(({ env }) => ({
    ```
-
+3. Update your `vite.config.ts` to include `"@auth/qwik"` to avoid potentials import issues
+```diff 
+   export default defineConfig(({ command, mode }): UserConfig => {
+  return {
+    plugins: [qwikCity(), qwikVite(), tsconfigPaths()],
+    // This tells Vite which dependencies to pre-build in dev mode.
+    optimizeDeps: {
+      include: ["@auth/qwik"],
+    },
+```
 
 
 ## Qwik API