Docker checks: remove emoji icons; handle "null" in license info; show rootless or not

docs/20_Checks/check_docker_info.md

@@ -15,13 +15,28 @@ This check sends performance data.
 icingaclient ALL=(ALL) NOPASSWD:SETENV: /usr/bin/docker
 ```
 
+## Includes
+
+Additional needed files in the current folder that this check can run:
+
+* inc_dockerfunctions.sh
+* inc_pluginfunctions
+
+## Rootless docker
+
+It works with docker setups as root and can handle rootless docker instances.
+
+To bring it up and running with an unpriviledged icinga user it must be able to access docker. Copy the docker binary eg. from /home/dockeruser/bin/docker to /usr/bin/. Then use the parameter `-p /usr/bin`.
+
+If DOCKER_HOST is not set then the docker socket is detected from a running docker instance and will be fetched from the process list.
+
 ## Syntax
 
 ```txt
 ______________________________________________________________________
 
 CHECK_DOCKER_INFO
-v1.2
+v1.3
 
 (c) Institute for Medical Education - University of Bern
 Licence: GNU GPL 3
@@ -81,7 +96,7 @@ None.
 `$ ./check_docker_info` returns
 
 ```txt
-OK: Docker 20.10.14 (Community Engine) .. containers: 2 running: 2 paused: 0 stopped: 0 .. images: 5
+OK: Docker 20.10.14 (Community Engine, rootless) .. containers: 2 running: 2 paused: 0 stopped: 0 .. images: 5
 All containers are running
  |containers-running=2;;;0;2 containers-paused=0;;;0;2 containers-stopped=0;;;0;2 images=33;;
 ```