docs: document admin environment variables (#11313)

www/apps/resources/app/integrations/guides/sanity/page.mdx

@@ -1454,8 +1454,8 @@ To configure the JS SDK, create the file `src/admin/lib/sdk.ts` with the followi
 import Medusa from "@medusajs/js-sdk"
 
 export const sdk = new Medusa({
-  baseUrl: "http://localhost:9000",
-  debug: process.env.NODE_ENV === "development",
+  baseUrl: import.meta.env.VITE_BACKEND_URL || "/",
+  debug: import.meta.env.DEV,
   auth: {
     type: "session",
   },