Show the example in the readme

Author: IvanUkhov

README.md

@@ -2,6 +2,26 @@
 
 The package provides wrappers for [LAPACKE].
 
+## Example
+
+```rust
+use lapacke::*;
+
+let n = 3;
+let mut a = vec![3.0, 1.0, 1.0, 1.0, 3.0, 1.0, 1.0, 1.0, 3.0];
+let mut w = vec![0.0; n as usize];
+let info;
+
+unsafe {
+    info = dsyev(Layout::ColumnMajor, b'V', b'U', n, &mut a, n, &mut w);
+}
+
+assert!(info == 0);
+for (one, another) in w.iter().zip(&[2.0, 2.0, 5.0]) {
+    assert!((one - another).abs() < 1e-14);
+}
+```
+
 ## Contribution
 
 Your contribution is highly appreciated. Do not hesitate to open an issue or a