I imagine you probably ran something like ember install ember-casper-template and then it would have thrown an error along the lines of:
➜ test-blog git:(master) ember install ember-casper-template
npm: Installed ember-casper-template
ENOENT: no such file or directory, scandir 'content/'
if you go this error then it is likely that ember didn’t get a chance to install the necessary packages automatically. Just run ember g ember-casper-template and it will do that for you 
I’ll take a look at making this a better experience for people wanting to try it out 