detailed and clearer readme for the opentrigger-board example

[Grienauer]

could we have a better readme text for the example "opentrigger-board"?
https://github.com/osdomotics/osd-contiki/tree/master/examples/osd/opentrigger-board

It would be great to have a readme show what the example does and how it works.
maybe link the wiki of the project if there it is a still an active development going on.