Add usage examples information

Author: cv21

README.md

@@ -1,3 +1,12 @@
 # jsonrpc2
 
-It is simple jsonrpc2 client.
+It is simple jsonrpc2 client.
+
+Usage:
+```go
+	client := NewClient(serverRpcUrl)
+	var val int
+	err := client.Call(context.Background(), "Divide", struct {
+		A,B int
+	}{4,2}, &val)
+```