Clarify that the docker group is created automatically (#4069)

engine/installation/linux/docker-ce/centos.md

@@ -145,6 +145,9 @@ from the repository.
     > which may not be appropriate for your stability needs.
     {:.warning}
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  On production systems, you should install a specific version of Docker CE
     instead of always using the latest. List the available versions. This
     example uses the `sort -r` command to sort the results by version number,
@@ -219,6 +222,9 @@ a new file each time you want to upgrade Docker.
     $ sudo yum install /path/to/package.rpm
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  Start Docker.
 
     ```bash

engine/installation/linux/docker-ee/centos.md

@@ -140,6 +140,9 @@ EE from the repository.
     > which may not be appropriate for your stability needs.
     {:.warning}
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  On production systems, you should install a specific version of Docker EE
     instead of always using the latest. List the available versions. This
     example uses the `sort -r` command to sort the results by version number,
@@ -166,6 +169,9 @@ EE from the repository.
     $ sudo yum install docker-ee-<VERSION>
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 4.  Edit `/etc/docker/daemon.json`. If it does not yet exist, create it. Assuming
     that the file was empty, add the following contents.
 
@@ -233,6 +239,9 @@ a new file each time you want to upgrade Docker.
     $ sudo yum install /path/to/package.rpm
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  Edit `/etc/docker/daemon.json`. If it does not yet exist, create it. Assuming
     that the file was empty, add the following contents.
 

engine/installation/linux/docker-ee/oracle.md

@@ -136,6 +136,9 @@ from the repository.
     $ sudo yum -y install docker-ee
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  On production systems, you should install a specific version of Docker
     instead of always using the latest. List the available versions.
     This example uses the `sort -r` command to sort the results by version
@@ -228,6 +231,9 @@ need to download a new file each time you want to upgrade Docker EE.
     $ sudo yum install /path/to/package.rpm
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  Edit `/etc/docker/daemon.json`. If it does not yet exist, create it. Assuming
     that the file was empty, add the following contents.
 

engine/installation/linux/docker-ee/rhel.md

@@ -197,6 +197,9 @@ from the repository.
     $ sudo yum -y install docker-ee-<VERSION_STRING>
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 4.  Edit `/etc/docker/daemon.json`. If it does not yet exist, create it. Assuming
     that the file was empty, add the following contents.
 
@@ -268,6 +271,9 @@ need to download a new file each time you want to upgrade Docker EE.
     $ sudo yum install /path/to/package.rpm
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 3.  Edit `/etc/docker/daemon.json`. If it does not yet exist, create it. Assuming
     that the file was empty, add the following contents.
 

engine/installation/linux/docker-ee/suse.md

@@ -184,6 +184,9 @@ from the repository.
     $ sudo zypper install docker-ee-<VERSION_STRING>
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 4.  Configure Docker EE to use the `btrfs` filesystem. **This is only required if
     the `/` filesystem is not using BTRFS.** However, explicitly specifying the
     `storage-driver` has no harmful side effects.
@@ -258,6 +261,9 @@ need to download a new file each time you want to upgrade Docker EE.
     $ sudo zypper install /path/to/package.rpm
     ```
 
+    Docker is installed but not started. The `docker` group is created, but no
+    users are added to the group.
+
 4.  Configure Docker EE to use the `btrfs` filesystem. **This is only required if
     the `/` filesystem is not using BTRFS.** However, explicitly specifying the
     `storage-driver` has no harmful side effects.