You can add it to your statusline (or tabline, ruler) with the wordcount() function:
:let &statusline ..= ' words: %{wordcount().words}'
---Aside: that "one-liner" doesn't "count the words in the file" at all? It just replaces all words with "1" and echos the last line number. I'm confused because this seems so wrong that I may be missing something? Unless the "67 substitutions on 5 lines" message is intended as the "word count", in which case I submit that 1) this is the ugliest thing I've ever seen, and 2) the author of this article doesn't know Vim all that well (there are so many better/easier ways to do this).