Update README.md to include sideload tutorial

Author: lukeblevins

README.md

@@ -6,6 +6,7 @@
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 <h3>Download Files</h3>
 <p>Files will eventually be available in the Microsoft Store, but you can <a href="https://drive.google.com/drive/folders/1cXCNPNoJWLj59lBV0SPxb5x3HYjphOFy?usp=sharing">download</a> a precompiled sideload package. Please note: these builds are unstable, incomplete, and only work on versions <b>1803 and 1809</b>. If you discover a bug, please fill out the form at <a href="https://goo.gl/forms/Z4bfKhaJJ6lT3Tcu2">this link</a>.</p> 
+<a href="https://youtu.be/1wSA8PYKhpA">Sideloading Files UWP Pre-Release Tutorial</a>
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 <img src="Assets/FeatureMap_Files.png" width="800px">