Consider adding examples of payment matching algorithm

[mattsaxon]

In show() step 8.1, an example would be useful, especially considering the language used isn't easy to pass e.g. "the second element of the tuple"

[marcoscaceres]

Might destructure the tuple into vars, for easier reading. I agree that "the second element of the tuple" is a bit confusing.

[marcoscaceres]

@mattsaxon, I've prepared a PR for this, but I'm reluctant to add an example there because we want implementers to implement from algorithms not examples.

See #530 and let me know if it's ok.

[mattsaxon]

@marcoscacares, thanks, happy with this.