feat(wpcarro/rust): Define Rc<T> example

My foray into "smart pointer" land.

Change-Id: I4ca775c72168dd34d90bf88fa41149867cd7fdae
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6244
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/scratch/rust/src/rc/mod.rs

@@ -0,0 +1,12 @@
+// Playing around with Rust's "smart pointers". Starting off with a wrapper type
+// that allows multiple readers (owners?) of some data.
+
+use std::rc::Rc;
+
+pub fn example() {
+    let five = Rc::new(5);
+    let x = Rc::clone(&five);
+    let y = Rc::clone(&five);
+    let z = Rc::clone(&five);
+    println!("result: {}", *x + *y + *z)
+}