atomic swap example in zoe docs does not fit with smart wallet architecture

[dckc]

This interaction isn't feasible with the messages clients can currently send to the chain:

documentation/main/guides/zoe/README.md

Lines 262 to 265 in a0bba25

	Even the creator of a contract instance needs an invitation to
	participate in it. Alice uses the returned `creatorInvitation` to
	make an offer, from which she gets an invitation that can be sent to
	the counter-party.

As part #726 , let's use the game places contract in place of atomic swap.

See also:

• handle invitation offer results in smart wallet agoric-sdk#8550