Add example to README

README.md

@@ -1,3 +1,31 @@
 # gl-init-rs
 
 Alternative to GLFW in pure Rust.
+
+## Usage
+
+```rust
+extern crate init = "gl-init-rs";
+extern crate libc;
+extern crate gl;
+
+fn main() {
+    use std::default::Default;
+
+    let window = init::Window::new(None, "Hello world!", &Default::default()).unwrap();
+
+    window.make_current();
+
+    gl::load_with(|symbol| window.get_proc_address(symbol) as *const libc::c_void);
+
+    gl::ClearColor(0.0, 1.0, 0.0, 1.0);
+
+    while !window.should_close() {
+        window.wait_events();
+
+        gl::Clear(gl::COLOR_BUFFER_BIT);
+
+        window.swap_buffers();
+    }
+}
+```