add import note

Author: morganchen12

firestore-next/test.firestore.js

@@ -2136,6 +2136,10 @@ describe("firestore-pipelines", () => {
 
     async function basicRead() {
       // [START basic_read]
+      // The import/require of "firebase/firestore/pipelines" has a side-effect
+      // of extending the Firestore class with the `.pipeline()` method.
+      // Without this import/require, you will not be able to create a Pipeline.
+      // import { execute } from "firebase/firestore/pipelines";
       const readDataPipeline = db.pipeline()
         .collection("users");
 

snippets/firestore-next/test-firestore/basic_read.js

@@ -5,6 +5,10 @@
 // 'npm run snippets'.
 
 // [START basic_read_modular]
+// The import/require of "firebase/firestore/pipelines" has a side-effect
+// of extending the Firestore class with the `.pipeline()` method.
+// Without this import/require, you will not be able to create a Pipeline.
+// import { execute } from "firebase/firestore/pipelines";
 const readDataPipeline = db.pipeline()
   .collection("users");