examples: Add a requestAnimationFrame loop example

guide/src/examples/request-animation-frame.md

@@ -0,0 +1,26 @@
+# `web-sys`: A `requestAnimationFrame` Loop
+
+[View full source code][code] or [view the compiled example online][online]
+
+[online]: https://rustwasm.github.io/wasm-bindgen/exbuild/request-animation-frame/
+[code]: https://github.com/rustwasm/wasm-bindgen/tree/master/examples/request-animation-frame
+
+This is an example of a `requestAnimationFrame` loop using the `web-sys` crate!
+It renders a count of how many times a `requestAnimationFrame` callback has been
+invoked and then it breaks out of the `requestAnimationFrame` loop after 300
+iterations.
+
+## `Cargo.toml`
+
+You can see here how we depend on `web-sys` and activate associated features to
+enable all the various APIs:
+
+```toml
+{{#include ../../../examples/request-animation-frame/Cargo.toml}}
+```
+
+## `src/lib.rs`
+
+```rust
+{{#include ../../../examples/request-animation-frame/src/lib.rs}}
+```