add missing lib

lib/ArduinoJson/CMakeLists.txt

@@ -0,0 +1,16 @@
+# ArduinoJson - arduinojson.org
+# Copyright Benoit Blanchon 2014-2018
+# MIT License
+
+cmake_minimum_required(VERSION 3.0)
+project(ArduinoJson)
+
+enable_testing()
+
+if(${COVERAGE})
+	set(CMAKE_CXX_FLAGS "-g -O0 -fprofile-arcs -ftest-coverage")
+endif()
+
+include_directories(${CMAKE_CURRENT_LIST_DIR}/src)
+add_subdirectory(third-party/catch)
+add_subdirectory(test)