docs ~ add example code

examples/ex.rs

@@ -0,0 +1,13 @@
+// `cargo run --example ex` (executes this example)
+
+use platform_info::*;
+
+fn main() {
+    let uname = PlatformInfo::new().unwrap();
+    println!("{}", uname.sysname());
+    println!("{}", uname.nodename());
+    println!("{}", uname.release());
+    println!("{}", uname.version());
+    println!("{}", uname.machine());
+    println!("{}", uname.osname());
+}