Add some instructions about Vagrant, notes about EC2 instance security and default users [ci skip]
Add some instructions about Vagrant, notes about EC2 instance security and default users [ci skip]

berkmancenter/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud