[Anno] Issues list in github

As a first step towards a new use case document for annotations, I created
an issues list in the github repository:

https://github.com/w3c/dpub-annotation/issues

Please add any other typos, missing use cases or other issues with the
current document for me to work through :)

Also, to reiterate, please do join the newly created web annotation working
group :)

Rob
-- 
Rob Sanderson
Technology Collaboration Facilitator
Digital Library Systems and Services
Stanford, CA 94305