Add a code of conduct doc. [ci skip]
Add a code of conduct doc. [ci skip]

jpalomar/underscore,akre54/underscore,rlugojr/underscore,tnga/underscore-es,jdelbello/underscore,akre54/underscore,keepgoingwm/underscore,jashkenas/underscore,jpalomar/underscore,jdelbello/underscore,keepgoingwm/underscore,documentcloud/underscore,rlugojr/underscore,tnga/underscore-es,jashkenas/underscore,documentcloud/underscore