docs: add new widevine requirements (#14024)

docs/tutorial/testing-widevine-cdm.md

@@ -2,6 +2,41 @@
 
 In Electron you can use the Widevine CDM library shipped with Chrome browser.
 
+Widevine Content Decryption Modules (CDMs) are how streaming services protect
+content using HTML5 video to web browsers without relying on an NPAPI plugin
+like Flash or Silverlight. Widevine support is an alternative solution for
+streaming services that currently rely on Silverlight for playback of
+DRM-protected video content. It will allow websites to show DRM-protected video
+content in Firefox without the use of NPAPI plugins. The Widevine CDM runs in an
+open-source CDM sandbox providing better user security than NPAPI plugins.
+
+#### Note on VMP
+
+As of [`Electron v1.8.0 (Chrome v59)`](https://electronjs.org/releases#1.8.1),
+the below steps are may only be some of the necessary steps to enable Widevine;
+any app on or after that version intending to use the Widevine CDM may need to
+be signed using a license obtained from [Widevine](https://www.widevine.com/)
+itself.
+
+Per [Widevine](https://www.widevine.com/):
+
+> Chrome 59 (and later) includes support for Verified Media Path (VMP). VMP
+> provides a method to verify the authenticity of a device platform. For browser
+> deployments, this will provide an additional signal to determine if a
+> browser-based implementation is reliable and secure.
+>
+> The proxy integration guide has been updated with information about VMP and
+> how to issue licenses.
+>
+> Widevine recommends our browser-based integrations (vendors and browser-based
+> applications) add support for VMP.
+
+To enable video playback with this new restriction,
+[castLabs](https://castlabs.com/open-source/downstream/) has created a
+[fork](https://github.com/castlabs/electron-releases) that has implemented the
+necessary changes to enable Widevine to be played in an Electron application if
+one has obtained the necessary licenses from widevine.
+
 ## Getting the library
 
 Open `chrome://components/` in Chrome browser, find `Widevine Content Decryption Module`