Added org-wc for counting words in org files

The [org-wc package](https://github.com/dato/org-wc) counts words in org files, ignoring org structure and only counting the "content".  I asked the maintainer if it could be put and MELPA and he agreed (see https://github.com/dato/org-wc/issues/3).  Package creation and installation works on my machine.

Thanks!