Update web extensions sample instructions

Author: brizental

samples/web-extension/README.md

@@ -10,13 +10,7 @@ Whenever this web extensions popup is opened it will trigger Glean.js events.
 
 ## How to run this sample
 
-1. Build Glean.js for web extensions. On the root folder of this repository run:
-
-```bash
-npm run build:webext
-```
-
-2. Generate metrics and pings files.
+1. Generate metrics and pings files.
 
 ```bash
 npm run glean_parser
@@ -26,6 +20,11 @@ npm run glean_parser
 > glean_parser is a Python package. To install it run `pip install glean_parser`.
 > Javascript support was added to glean_parser on version 2.1.0, make sure your version is up to date.
 
+2. Link the `@mozilla/glean` package. On this `web-extension` folder run:
+
+```bash
+npm link @mozilla/glean
+```
 
 3. Build this sample. On this `web-extension` folder run:
 

samples/web-extension/index.js

@@ -4,7 +4,7 @@
 
 "use strict";
 
-import Glean from "glean";
+import Glean from "@mozilla/glean/webext";
 import { custom } from "./generated/pings";
 import { webextStarted, popupOpened } from "./generated/sample";