updated terminology.md
updated terminology.md

Broke this down into terminology and roles. Both of these things used to be on the front page but since that document was ridiculously long, I moved them here and people can read this before they begin. Also clarified what 'airgap' and 'sneakernet' mean, as suggested by @dolanjs
pwplus/securedrop,ageis/securedrop,harlo/securedrop,micahflee/securedrop,heartsucker/securedrop,jrosco/securedrop,jeann2013/securedrop,heartsucker/securedrop,pwplus/securedrop,chadmiller/securedrop,chadmiller/securedrop,heartsucker/securedrop,jaseg/securedrop,heartsucker/securedrop,kelcecil/securedrop,GabeIsman/securedrop,conorsch/securedrop,ehartsuyker/securedrop,micahflee/securedrop,harlo/securedrop,jeann2013/securedrop,ageis/securedrop,kelcecil/securedrop,jrosco/securedrop,ageis/securedrop,jrosco/securedrop,kelcecil/securedrop,kelcecil/securedrop,chadmiller/securedrop,jaseg/securedrop,jrosco/securedrop,GabeIsman/securedrop,jrosco/securedrop,conorsch/securedrop,GabeIsman/securedrop,micahflee/securedrop,jaseg/securedrop,chadmiller/securedrop,ehartsuyker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,kelcecil/securedrop,GabeIsman/securedrop,pwplus/securedrop,harlo/securedrop,jaseg/securedrop,ehartsuyker/securedrop,garrettr/securedrop,conorsch/securedrop,harlo/securedrop,garrettr/securedrop,jaseg/securedrop,ehartsuyker/securedrop,conorsch/securedrop,GabeIsman/securedrop,jrosco/securedrop,chadmiller/securedrop,harlo/securedrop,ageis/securedrop,jeann2013/securedrop,jeann2013/securedrop,GabeIsman/securedrop,pwplus/securedrop,conorsch/securedrop,heartsucker/securedrop,pwplus/securedrop,jeann2013/securedrop,jeann2013/securedrop,kelcecil/securedrop,jaseg/securedrop,garrettr/securedrop,harlo/securedrop,pwplus/securedrop,garrettr/securedrop,chadmiller/securedrop,ehartsuyker/securedrop