Fix url in Dockerfile instructions

Fixes #2

Dockerfile

@@ -2,7 +2,7 @@
 # Create an empty directory and cd inside it.
 # Get the source code from dt_ctrl in a subdirectry, e.g. through git:
 # ```
-# git clone gitlab.camras.nl/dijkema/dt_ctrl
+# git clone https://gitlab.camras.nl/dijkema/dt_ctrl
 # ```
 # Create the docker file with `docker build --tag consoledemo .`
 # This Dockerfile is hardcoded to run the websockets server at