Fix readme after Docker compose cleanup

See merge conflict markers, etc in https://gitlab.com/gitlab-org/gitter/webapp/merge_requests/1084/diffs#8ec9a00bfd09b3190ac6b22251dbb1aa95a0579d_1_1
5 jobs for feature/fix-readme-after-docker-refactor in 11 minutes and 57 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build Unit Test
passed #31910790
package

00:05:00

passed #31910789
test

00:11:30

passed #31910788
validate

00:01:16

 
  Deploy
failed #31910791
allowed to fail
containerize

00:00:10

passed #31910793
deploy_beta_staging

00:00:27

 
Name Stage Failure
failed
containerize Deploy There is an unknown failure, please try again
total 4
drwxrwxrwx 3 root root 16 Sep 10 03:34 .
drwxrwxrwx 18 root root 4096 Sep 10 03:34 ..
drwxrwxrwx 2 root root 20 Sep 10 03:34 app
$ docker login -u gitlab-ci-token -p $CI_JOB_TOKEN registry.gitlab.com
WARNING! Using --password via the CLI is insecure. Use --password-stdin.
Warning: failed to get default registry endpoint from daemon (Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?). Using system default: https://index.docker.io/v1/
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
ERROR: Job failed: exit code 1