Mention dependency on `users`

[skandragon]

In the browser console:

    at constellation_console.js?hash=330bd3efe63ae25e305c104e000a0904527646d5:1218
    at Computation._compute (tracker.js:308)
    at new Computation (tracker.js:206)
    at Object.Tracker.autorun (tracker.js:576)
    at constellation_console.js?hash=330bd3efe63ae25e305c104e000a0904527646d5:1217
    at maybeReady (meteor.js?hash=857dafb4b9dff17e29ed8498a22ea5b1a3d6b41d:938)
    at HTMLDocument.loadingCompleted (meteor.js?hash=857dafb4b9dff17e29ed8498a22ea5b1a3d6b41d:950)

Fix: meteor add accounts-base (or similar)

[JackAdams]

Ahh... good point.