readme: Add an example to the readme

sysvmq/README.md

@@ -1,9 +1,19 @@
 # Sysvmq
 
-This aims to be a easy usable API for SysV IPC message queues.
+This library provides a convenient and easy usable API for SysV IPC
+message queues.
 
-    Note: This library is work in progress.
+```rust
+use sysvmq::{SysvMq, SysvMqError};
 
-Currently supported operations are only `create` and `unlink`. The
-`create` operation creates a SysV IPC message queue and the `unlink`
-operation deletes such a SysV IPC message queue.
+fn example() -> Result<(), SysvMqError> {
+    let mut mq = SysvMq::new(0)?;
+    let mut buf = [0u8; 11];
+
+    mq.send(b"hello queue")?;
+    mq.recv(&mut buf)?;
+    mq.delete()?;
+
+    Ok(())
+}
+```