add readme

readme.md

@@ -1,3 +1,22 @@
-```js
-    import { deepCopy } from 'fast-deep-copy'
+#   fast-deep-copy 
+    Only 20 lines code! no deps!
+
+useage:
+```
+    npm install -S fast-deep-copy
+```
+
+```js
+
+    import { deepCopy } from 'fast-deep-copy'
+
+    let a = { dataA: 10, b: null };
+    let b = { dataB: 20, a: null };
+    a.b = b;
+    b.a = a;
+
+    let newA = deepCopy(a);
+    console.log(newA.dataA === 10);     //true
+    console.log(newA.b.dataB === 20);   //true
+    console.log(newA.b.a === newA);     //true
 ```