Doc: update NR 1.8.2.3 Text alignment

As noted by Phil Holmes on -devel, the bit
about \null and invisible anchor points being
absolutely required is no longer true.

Also, \hspace and \vspace were not explained in
that section although these are hugely popular and
useful commands. That commit addresses both points.

Also: paging Dr @tdanielsmusic for proofreading :-)