docs: Revise before_you_begin.rst
docs: Revise before_you_begin.rst

conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ehartsuyker/securedrop