client: update documentation about threading
Remove out-dated documentation and add few more words
about this topic.
v2. replace a paragraph by better explanation from Pekka Paalanen
fix other notes from reviewing
v3. fix typo
v4. fix flags for poll in an example
add wl_display_cancel_read() to another example
(so that user sees that it should be used)
move proper use of wl_display_prepare_read
before the explanation why it is wrong to use
wl_display_displach
Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>