Update README.md with PRINT_JSON option

README.md

@@ -58,6 +58,11 @@ at something that was already corrected, run
 inside the `build` directory and cmake again.
 
 ### building and compiling ###
-As above.
+When compiling and executing the agent locally, in order to see the resulting
+JSON objects, run cmake with the option `PRINT_JSON`
 
-TODO: add DEBUG or DEV option.
+	$ cmake -DPRINT_JSON=ON ..
+
+You may also set the `Debug` flag if using gdb
+
+    $ cmake -DCMAKE_BUILD_TYPE=Debug -DPRINT_JSON=ON ..