SPEC.md: "container" env variable
SPEC.md: "container" env variable

In likeness to other existing container technologies, an enviroment
variable of `container` set to the name of the runtime tool. Prior tool
examples include "lxc", "systemd-nspawn", "lxc-libvirt".

iaguis/appc-spec,3ofcoins/appc-spec,dustymabe/spec,craimbert/spec,marineam/spec,krnowak/appc-spec,dgonyeo/spec,squeed/spec,ChengTiesheng/spec,endocode/appc-spec,appc/spec,squeed/spec,stufflebear/spec,endocode/appc-spec,iaguis/appc-spec,yifan-gu/spec,alban/appc-spec,3ofcoins/appc-spec,krnowak/appc-spec,tklauser/spec,appc/spec,tklauser/spec,dustymabe/spec,jonboulle/spec,ChengTiesheng/spec,jonboulle/spec,jonboulle/spec,krnowak/appc-spec,dustymabe/spec,stufflebear/spec,endocode/appc-spec,yifan-gu/spec,apcera/appc-spec,dgonyeo/spec,stufflebear/spec,tklauser/spec,craimbert/spec,iaguis/appc-spec,squeed/spec,apcera/appc-spec,3ofcoins/appc-spec,yifan-gu/spec,alban/appc-spec,dgonyeo/spec,ChengTiesheng/spec,zenlinTechnofreak/spec,craimbert/spec,zenlinTechnofreak/spec,apcera/appc-spec,marineam/spec,zenlinTechnofreak/spec,alban/appc-spec,marineam/spec,appc/spec