Add docs to gitignore.
Add docs to gitignore.

laurenrevere/ember-preprints,baylee-d/ember-preprints,CenterForOpenScience/ember-preprints,baylee-d/ember-preprints,laurenrevere/ember-preprints,caneruguz/ember-preprints,CenterForOpenScience/ember-preprints,caneruguz/ember-preprints