[profgui] Suggest for related work section

I suggest replacing the section that now is headed "Related work" with a
header saying "Profile types" and with the text in
https://github.com/w3c/dxwg/issues/435#issuecomment-426928897.

I also think we can expand that a bit to talk about the motivation for
creating profiles. The introduction to that section could attempt to
answer the question: why do people create profiles?

If folks are ok with this, I'll make the change. If you are ok with it
in general but want to see wording changes, let's do that in the github
issue.

kc
-- 
Karen Coyle
kcoyle@kcoyle.net http://kcoyle.net
m: 1-510-435-8234 (Signal)
skype: kcoylenet/+1-510-984-3600