137 and 132 more distractions

Hi folks

issue   137 <https://github.com/w3c/coga/issues/137> has Avoid busy
patterns because they are visually confusing . Issue 132 adds that they are
distracting. They also mention noices

I suggest we add:

   - to 4.6.1.1  avoid interruptions  : distracting backgrounds, soft and
   loud noises
   - in  4.6.1.1 how it works section we can add: Some people are sensitive
   to noise and can easily become overwhelmed by too many stimuli.
   - also we could add to 4.6.3 Avoid Too Much Content we can add to the
   description  "Keep the interface simple".

We can also tag this issue for the next version. It needs more research etc
to be done correctly.

All the best
Lisa