add note about SELinux and Docker Desktop

Signed-off-by: Simon L <szaimen@e.mail.de>

Containers/mastercontainer/start.sh

@@ -61,6 +61,8 @@ fi
 # Check if api version is supported
 if ! sudo -u www-data docker info &>/dev/null; then
     print_red "Cannot connect to the docker socket. Cannot proceed."
+    echo "If you are on Docker Desktop v4.19 or higher, see https://github.com/nextcloud/all-in-one/issues/2450"
+    echo "If SELinux is enabled on your host, see https://github.com/nextcloud/all-in-one#how-to-change-the-default-location-of-nextclouds-datadir#are-there-known-problems-when-selinux-is-enabled"
     exit 1
 fi
 API_VERSION_FILE="$(find ./ -name DockerActionManager.php | head -1)"

readme.md

@@ -264,6 +264,9 @@ Afterwards it should work.<br>
 
 See https://dev.to/ozorest/fedora-32-how-to-solve-docker-internal-network-issue-22me for more details on this. This limitation is even mentioned on the official firewalld website: https://firewalld.org/#who-is-using-it
 
+### Are there known problems when SELinux is enabled?
+Yes. If SELinux is enabled, you might need to add the `--security-opt label=disabled` option to the docker run command of the mastercontainer in order to allow it to access the docker socket. See https://github.com/nextcloud/all-in-one/discussions/485
+
 ### How to run `occ` commands?
 Simply run the following: `sudo docker exec --user www-data -it nextcloud-aio-nextcloud php occ your-command`. Of course `your-command` needs to be exchanged with the command that you want to run.