[PATCH wayland] doc: Fill in high level description for Surfaces

[Bill Spitzak]

I think talking about a surface having multiple buffers is misleading.

A wl_surface only knows about one buffer after commit: the last buffer 
attached to it. The wording being proposed here makes it sound like the 
surface keeps track of the previous buffer and expects or requires it to 
be used in the next attach.

I think the problem with the docs right now is that a lot of wl_surface 
requests say "foo is double-buffered state, see wl_surface.commit". The 
word double-buffered unfortunately immediately makes people think only 
about pixel buffers, even though in fact it is other data that is being 
double-buffered.

I would avoid the use of the term "double buffered". Possible 
alternative: "The change does not happen until the next 
wl_surface.commit." All current talk about double-buffering in commit 
should use words like "deferred" or "pending" instead.