Version this guide and create tags

[jessestricker]

Assigning a version to this evolving guide allows people to check more easily what changed since they last visited and whether they should align their systems.

This doesn't need to be complicated and I think semantic versioning isn't really applicable here.
But even just an increasing number between logical groups of changes will go along way on helping readers keep up with additions or changes to this great guide.

If this gets implemented, a Git tag (or even better a GitHub Release) for every version will be nice.
Then users can use the GitHub "Watch Custom -> Release" feature and get notifications.