ada/9406: Documentation suggestion

[Ben Elliston]

>>>>> "Geert" == Geert Bosch <bosch@gnat.com> writes:

  >> I see your point about partitions though I must say it was far from
  >> obvious that I should be looking there. Perhaps the UM should have a
  >> reference to the RM.

  Geert> I now see what you mean. I agree that the language here could
  Geert> be improved. Actually, the language from the Ada RM that I
  Geert> quoted seems to be pretty clear, so I think we should borrow
  Geert> from that or indeed put in a link (or both).

I'm not an Ada language lawyer, so the scope of this PR is a bit
beyond me now.  I will commit the simple grammar fix and then put the
PR back into analysed state so that it can be finished off by one of
you fellows.

Cheers, Ben