1. just release a build script like(build.xml for ant or pom.xml for maven, which should already be generate for you by your IDE)
2. just pick one from http://www.codinghorror.com/blog/2007/04/pick-a-license-any-license.html
. then download the license text as a textfile from the offical website(google) and upload it to your github repo, or write in the readme that licsense XY is used.
Then of course you can also state that the models and textures are not part of the license and normal copyright applys