revise the AMT pages in the documentation

[davidschlangen]

Section 10 ("Getting participants from Amazon Mechanical Turk") could profit from a thorough revision. It currently presupposes a lot of knowedge of AMT / HITs, and also is somewhat difficult to follow in terms of language. Here it would be good to talk readers through an actual examples. Like, what would you need to do if you wanted to collect people from AMT just to bring them together in a chat room (no additional bot besides the concierge bot)? [Or maybe set up a super simple bot just for this example; maybe the bot just tells the two dialogue participants after n minutes that they have now done enough, and gives them a token to enter into the AMT interface.]