Create thanks.md

Created in the style of [thanks.md](https://github.com/paulmolluzzo/thanks-md) from [this suggestion on Twitter](https://twitter.com/b0rk/status/968225634127372288).

Author: alexkadis

thanks.md

@@ -0,0 +1,6 @@
+# User Testimonials
+
+In this file, you can read about where and how people use Rubberduck:
+
+- Edit this file, and tell us why you like Rubberduck. - [@username](https://github.com/username)
+- Edit this file, and tell us why you like Rubberduck. - [@username](https://github.com/username)