intro: add URLs

intro/index.rst

@@ -6,6 +6,11 @@ Introduction
 Welcome to the BeagleBoard documentation project. If you are looking for help with your Beagle
 open-hardware development platform, you've found the right place!
 
+For the latest versions of this documentation, be sure to check the official release sites:
+
+* https://docs.beagle.cc (cached with local proxies)
+* https://docs.beagleboard.org (non-cached, without proxies)
+
 Please check out our :ref:`support` page` to find out how to get started, resolve issues,
 and engage the developer community.