Add doc-comment example script.

scripts/doc-comments.rhai

@@ -0,0 +1,20 @@
+/// The function `foo`, which prints `hello, world!` and a magic number,
+/// accepts three parameters.
+///
+/// # Parameters
+///
+/// `x` - `i64`  
+/// `y` - `string`  
+/// `z` - `bool`
+///
+/// # Notes
+///
+/// This is a doc-comment.  It can be obtained with the `metadata` feature.
+///
+/// An example is the `rhai-doc` app.
+///
+fn foo(x, y, z) {
+   print(`hello, world! ${if z { x + y.len() } else { x } }`);
+}
+
+foo(39, "bar", true);