git-node: update WPT fixtures README template (#297)

* git-node: update WPT fixtures README template

Author: joyeecheung

lib/wpt/templates/README.md

@@ -1,9 +1,16 @@
 # Web Platform Test Fixtures
 
-The fixtures here are pulled from https://github.com/web-platform-tests/wpt
-using [`git node wpt`](https://github.com/nodejs/node-core-utils/blob/master/docs/git-node.md#git-node-wpt)
+The files in this folder, including this document,
+are generated by [`git node wpt`][].
 
+This folder contains a subset of the [Web Platform Tests][] for the
+implementation of Web APIs in Node.js.
+
+See [test/wpt](../../wpt/README.md) for information on how these tests are run.
 
 Last update:
 <% for (const [path, url] of map) { %>
 - <%= path %>: <%= url %><% } %>
+
+[Web Platform Tests]: https://github.com/web-platform-tests/wpt
+[`git node wpt`]: https://github.com/nodejs/node-core-utils/blob/master/docs/git-node.md#git-node-wpt