README: layer dependencies should be master

The layer dependencies for the master branch should be to master
branches

Signed-off-by: John Weber <rjohnweber@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
wandboard: Remove me as maintainer

I will not have time to spend to maintain and test the Wandboard
machines, so remove me as maintainer.

Signed-off-by: John Weber <rjohnweber@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>