Added examples.

examples/playground/src/main.rs

@@ -0,0 +1,7 @@
+//! The playground example is a special example meant for unstructured experimentation which can potentially be turned
+//! into an actual example at some point or deleted. It should always be reset to unchanged hello world before the working
+//! branch where the experimentation is happening is merged.
+
+fn main() {
+    println!("Hello, world!");
+}