bug#63726: time-machine without options does not get the latest commit

[Konrad Hinsen]

Hi,

> Should we fix the doc or should we fix the code?…

I vote for fixing the doc. Two reasons:

 1. Having "guix time-machine" and "guix pull" behave in the same way
    is desirable. Less cognitive load for users.

 2. What the doc says cannot be implemented in general. "The latest
    commit on the master branch" makes no sense for a setup with
    multiple channels, some of which may not even have a branch called
    "master".

Cheers,
  Konrad.