I went to find a reference for the new recommended behavior in the
sources, and ended up had to refer to D92522 to determine where it ended
up (i.e. ProgrammersManual.rst).
At the risk of the two copies diverging, it seemed useful to note the
new recommended use of SmallVector directly at the class declaration,
and also get the benefit of it appearing in a slightly emphasized way in
the rendered Doxygen.