Make dev fails on Debian 9 Qubes

On behalf of pierwill, copy/pasted from a comment:

In a Debian-9 qube, I’m getting this error when running make images dev:

user@securedrop:~/securedrop/securedrop$ make images dev
docker build  -f Dockerfile -t securedrop-test:cd2a785bdc3d83e5997e35fcecebd47f7882c8c8 .
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.35/build?buildargs=%7B%7D&cachefrom=%5B%5D&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels=%7B%7D&memory=0&memswap=0&networkmode=default&rm=1&session=30d8d4489fba73e40fd9f779e3ae0ca7d27d0bb1969636836eac24439142861c&shmsize=0&t=securedrop-test%3Acd2a785bdc3d83e5997e35fcecebd47f7882c8c8&target=&ulimits=null: dial unix /var/run/docker.sock: connect: permission denied
Makefile:18: recipe for target 'images' failed
make: *** [images] Error 1

Things work fine when running sudo make images dev. Is this expected? Should I update the doc noting sudo might be necessary?

By default docker can only be run by root, but you can follow the post installation steps to allow users to run the docker command. It would probably be a good thing to add that link to the documentation.