Add gitignore to generated app
Add gitignore to generated app

This fixes the Ember CLI “maxBuffer” error. When adding files to git,
the list of added files is written to stdout. Because node_modules was
not in .gitignore, that list exceeded execa’s 10MB buffer. (lol)
glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js