Linking the Wiki to the example Flows

Part of today's discussion was about how to have more readily viewable
versions of the flows in the Github repo.  I have added an example link to
the bottom of the flows section of the wiki page at [1]. Basically this is
a simple Markdown link to a web service that then renders the diagram.  The
web service is hosted on one of my machines, but that's fine.  I don't
anticipate a lot of load ;-)

The format for the URI is:

    http://pandora.aptest.com:8090/plantuml/proxy?format=svg&src=

Followed by the URI of the raw plantuml source in the github repo for
whatever flow you want to show.

[1] https://github.com/w3c/webpayments/wiki/Flows

-- 
-Shane