add mergedata() example

[atsaloli]

bundle agent main
{
  vars:
      "global" data => parsejson('{ "fruit": "banana", "drink": "pepsi" }');
      "override" data => parsejson('{ "drink": "coke" }');

      "merged_global_and_override" data => mergedata("global", "override");
      "merged_global_and_override_str" string => format("%S", merged_global_and_override);
  reports:
      "$(merged_global_and_override_str)";
}

output:

test.cf                                                                                                                                                                                                                                      
[root@host ~]# cf-agent -f ./test.cf

R: {"drink":"coke","fruit":"banana"}
[root@host ~]#