add README

Chromecast/README.md

+# Chromecast sample
+
+### Prerequisite
+- Your device/simulator must be connected to wifi and have internet
+- A chromecast must be setup on your local wifi network
+
+### Possible improvements
+- Use a crossplatform filepicker to cast local files
+- List local files in a crossplatform way
+- List all discovered chromecasts
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RecordHLS/README.md

+# RecordHLS sample
+
+### Possible improvements
+- Add support for .NET Core mac/linux
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