Wekan docker image failing to run

Hey all, looking at trying out Wekan so I thought I'd give the docker image a spin, but it crashes with a stack trace:

/build/programs/server/boot.js:468
  }).run();
     ^
Error: Must pass options.rootUrl or set ROOT_URL in the server environment
    at Object.Meteor.absoluteUrl (packages/meteor.js:1378:11)
    at runWebAppServer (packages/webapp/webapp_server.js:798:18)
    at packages/webapp/webapp_server.js:1219:1
    at module (packages/webapp/webapp_server.js:1219:16)
    at fileEvaluate (packages/modules-runtime.js:336:7)
    at Module.require (packages/modules-runtime.js:238:14)
    at require (packages/modules-runtime.js:258:21)
    at /build/programs/server/packages/webapp.js:1658:15
    at /build/programs/server/packages/webapp.js:1667:3
    at /build/programs/server/boot.js:401:38
    at Array.forEach (<anonymous>)
    at /build/programs/server/boot.js:226:21
    at /build/programs/server/boot.js:464:7
    at Function.run (/build/programs/server/profile.js:280:14)
    at /build/programs/server/boot.js:463:13

I can't find anything on the Docker hub page that explains any settings I need to pass, just wondering if I've missed something?