user-manual: update for new default --track behavior
user-manual: update for new default --track behavior

Update documentation to reflect the --track default.

That change seems to have happened in the 1.5.3 -rc's, so bump the "for
version x.y.z or newer" warning as well.

Signed-off-by: J. Bruce Fields <51738506c1b2ccb0761f23bdc612c93babf738ea@citi.umich.edu>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git