Add release to README.md

Author: Joy-less

README.md

@@ -1,5 +1,7 @@
 # JsonhCpp
 
+[![C++](https://img.shields.io/github/release/jsonh-org/JsonhCpp.svg?style=flat-square&label=c%2b%2b)](https://github.com/jsonh-org/JsonhCpp/releases)
+
 **JSON for Humans.**
 
 JSON is great. Until you miss that trailing comma... or want to use comments. What about multiline strings?