Revert "Temporarily stop listing the official Chrome extension in the main README"

This reverts commit afabbc28c5.

README.md

@@ -38,6 +38,8 @@ PDF.js is built into version 19+ of Firefox.
 
 #### Chrome
 
++ The official extension for Chrome can be installed from the [Chrome Web Store](https://chrome.google.com/webstore/detail/pdf-viewer/oemmndcbldboiebfnladdacbdfmadadm).
+*This extension is maintained by [@Rob--W](https://github.com/Rob--W).*
 + Build Your Own - Get the code as explained below and issue `gulp chromium`. Then open
 Chrome, go to `Tools > Extension` and load the (unpackaged) extension from the
 directory `build/chromium`.

gulpfile.js

@@ -2367,5 +2367,9 @@ gulp.task("externaltest", function (done) {
 
 gulp.task(
   "ci-test",
-  gulp.series(gulp.parallel("lint", "externaltest", "unittestcli"), "typestest")
+  gulp.series(
+    gulp.parallel("lint", "externaltest", "unittestcli"),
+    "lint-chromium",
+    "typestest"
+  )
 );