Update README.md

Author: levkopo

README.md

@@ -1,2 +1,15 @@
 # executor-json-library
  Simple json library for KayJam Executor
+
+## How to use
+### Decode
+```
+var jsonEncoded = "{\"test\":123}"
+var decoded = JSON::decode(jsonEncoded);
+
+println(decoded);
+```
+Output: 
+```
+[test:123]
+```