Add readme to Example folder (#21119)

Adding a readme file that warns people not to use these examples as
examples of how to use Fluid Framework.

examples/README.md

@@ -0,0 +1,13 @@
+# Fluid Framework Examples
+
+**Note: These examples are for internal consumption only and should not be used to build Fluid Framework apps.**
+
+This repository contains a collection of examples that are intended for internal use and serve as a
+reference for developers working on the Fluid Framework. Many of the APIs used in these examples are NOT part
+of the public API surface and the coding patterns here do not represent the recommended ways to use Fluid Framework.
+Go to [microsoft/FluidExamples](https://github.com/microsoft/fluidexamples) for examples of how to use Fluid Framework.
+
+## License
+
+This repository is licensed under the [MIT License](LICENSE). However, please note that the examples provided
+here are for internal use only and should not be used to build Fluid Framework apps.