add arduino json lib

#182

lib/ArduinoJson/CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contribution to ArduinoJson
+
+First, thank you for taking the time to contribute to this project.
+
+You can submit changes via GitHub Pull Requests.
+
+Please:
+
+1. Unit test every change in behavior
+2. Use clang-format in "file" mode to format the code
+3. Consider using the Continuous Integration (Travis and AppVeyor)