docs: make sure vm.max_map_count >= 262144
@@ -23,6 +23,7 @@ $ docker-compose up # Run RackHD and ELK.
**Prerequisites:**
* docker v1.10 or higher
* docker-compose v1.6 or higher [Install Docker Compose](https://docs.docker.com/compose/install/)
+ * Please make sure vm.max_map_count >= 262144 ```sudo sysctl -w vm.max_map_count=262144```
```
$ cd RackHD/docker
