Make use of git tags and github releases

[jvoisin]

The readme says "Napkin v1.5", but the tags and releases sections are empty.

It would be nice to do actual releases :)

[vEnhance]

I think this would make sense if I got to actively writing the text again. Unfortunately for the past years I haven't found the energy to do so and most of the commits are just typo fixes and the like, so I think in that case it makes less sense to try and apply tags at the moment.

[jvoisin]

Then it would be nice to tag a 1.0 to signal that the document has reached stability.

[vEnhance]

@Incompleteusern once #210 is merged maybe we can tag that as v1.5?