Add support note to selinux option

README.md

@@ -145,7 +145,7 @@ additional details on each available environment variable.
 | `ECS_RESERVED_MEMORY` | 32 | Reduction, in MiB, of the memory capacity of the instance that is reported to Amazon ECS. Used by Amazon ECS when placing tasks on container instances. This doesn't reserve memory usage on the instance. | 0 | 0 |
 | `ECS_AVAILABLE_LOGGING_DRIVERS` | `["awslogs","fluentd","gelf","json-file","journald","logentries","splunk","syslog"]` | Which logging drivers are available on the container instance. | `["json-file","none"]` | `["json-file","none"]` |
 | `ECS_DISABLE_PRIVILEGED` | `true` | Whether launching privileged containers is disabled on the container instance. | `false` | `false` |
-| `ECS_SELINUX_CAPABLE` | `true` | Whether SELinux is available on the container instance. | `false` | `false` |
+| `ECS_SELINUX_CAPABLE` | `true` | Whether SELinux is available on the container instance. (Limited support; Z-mode mounts only.) | `false` | `false` |
 | `ECS_APPARMOR_CAPABLE` | `true` | Whether AppArmor is available on the container instance. | `false` | `false` |
 | `ECS_ENGINE_TASK_CLEANUP_WAIT_DURATION` | 10m | Default time to wait to delete containers for a stopped task (see also `ECS_ENGINE_TASK_CLEANUP_WAIT_DURATION_JITTER`). If set to less than 1 second, the value is ignored.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3h | 3h |
 | `ECS_ENGINE_TASK_CLEANUP_WAIT_DURATION_JITTER` | 1h | Jitter value for the task engine cleanup wait duration. When specified, the actual cleanup wait duration time for each task will be the duration specified in `ECS_ENGINE_TASK_CLEANUP_WAIT_DURATION` plus a random duration between 0 and the jitter duration. | blank | blank |