Document that ENV vars are not automatically updated
Document that ENV vars are not automatically updated

Unlike the entries in `/etc/hosts`, environment-variables for linked
containers are not automatically updated if the linked container is
restarted.

This adds a note to the documentation in;
https://docs.docker.com/userguide/dockerlinks/#environment-variables
and
https://docs.docker.com/reference/run/#env-environment-variables

To make users aware that this is the case and recommends them to use
the `/etc/hosts` entries in stead.

I added this change because users were expecting environment variables
to be updated automatically as well (https://github.com/docker/docker/issues/10164).

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

riyazdf/cli,redpanda/cli,thaJeztah/cli,allencloud/cli,ashfall/cli,dnephin/cli,dnephin/cli,ashfall/cli,e11137/cli,Zebrilee/cli,e11137/cli,cpuguy83/cli,Zebrilee/cli,redpanda/cli,cpuguy83/cli,thaJeztah/cli,allencloud/cli,riyazdf/cli,docker/cli,docker/cli