Add changelog for 0.4
Add changelog for 0.4

garrettr/securedrop,micahflee/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,micahflee/securedrop,heartsucker/securedrop,garrettr/securedrop,micahflee/securedrop,ehartsuyker/securedrop,micahflee/securedrop,conorsch/securedrop,garrettr/securedrop