Start versioning the guide

[MichaelChirico]

We have a DESCRIPTION file with a Version entry:

https://github.com/tidyverse/style/blob/adbdbb7a9456585579f5e5351e0c3b535e129d34/DESCRIPTION#L3

But that hasn't changed in 7 years 🙃.

I think it will be helpful for downstream consumers of the guide if we can mark some "lines in the sand" of update activity to the guide by bumping the version (whether in this DESCRIPTION file or elsewhere).

[hadley]

And we need a news file.

[MichaelChirico]

We could also add a DOI