docs: Clarify mesos driver, also line-wrapping

Signed-off-by: Ahmet Alp Balkan <[email protected]>

cluster/mesos/README.md

@@ -1,40 +1,59 @@
 # Using Docker Swarm and Mesos
 
-Swarm comes with a built-in scheduler that works with the swarm manager to schedule container resources. You can completely replace the built-in scheduler with a 3rd party scheduler. For example, you can replace it with the Mesos scheduler as described here.
+Swarm comes with a built-in scheduler that works with the swarm manager to
+schedule container resources. You can completely replace the built-in scheduler
+with a 3rd party scheduler. For example, you can replace it with the Mesos
+scheduler as described here.
 
 When using Docker Swarm and Mesos, you use the Docker client to ask the swarm
 manager to schedule containers. The swarm manager then schedules those
 containers on a Mesos cluster.
 
 ## Prerequisites
 
-Each node in your swarm must run a Mesos slave. The slave must be capable of starting tasks in a Docker Container using the `--containerizer=docker` option.
+Each node in your swarm must run a Mesos slave. The slave must be capable of
+starting tasks in a Docker Container using the `--containerizer=docker` option.
 
-You need to configure two TCP ports on the slave. One port to listen for the swarm manager, for example 2375. And a second TCP port to listen for the Mesos master, for example 3375.
+You need to configure two TCP ports on the slave. One port to listen for the
+swarm manager, for example 2375. And a second TCP port to listen for the Mesos
+master, for example 3375.
 
 ## Start the Docker Swarm manager
 
 If you use a single Mesos master:
 
 ```     
-docker run -d -p <swarm_port>:2375 -p 3375:3375 swarm manage -c mesos-experimental --cluster-opt mesos.address=<public_machine_ip> --cluster-opt mesos.port=3375 <mesos_master_ip>:<mesos_master:port>
+$ docker run -d -p <swarm_port>:2375 -p 3375:3375 \
+    swarm manage \
+        -c mesos-experimental \
+        --cluster-opt mesos.address=<public_machine_ip> \
+        --cluster-opt mesos.port=3375 \
+        <mesos_master_ip>:<mesos_master:port>
 ```
 
-If you use multiple Mesos masters:
-
-```
-docker run -d -p <swarm_port>:2375 -p 3375:3375 swarm manage -c mesos-experimental --cluster-opt mesos.address=<public_machine_ip> --cluster-opt mesos.port=3375 zk://<mesos_masters_url>
-```
+The command above creates a swarm manager listening at `<swarm_port>`.
+The `<mesos_master_ip>` value points to where Mesos master lives in the cluster.
+Typically, this is localhost, a hostname, or an IP address.  The `<public_machine_ip>`
+value is the IP address for Mesos master to talk to swarm manager. If mesos master
+and swarm manager are co-located on the same machine, you can use the `0.0.0.0`
+or `localhost` value.
 
-Once the manager is running, check your configuration by running `docker info` as follows:
+If you use multiple Mesos masters:
 
 ```
-docker -H tcp://<manager_ip:manager_port> info
+$ docker run -d -p <swarm_port>:2375 -p 3375:3375 \
+    swarm manage \
+        -c mesos-experimental \
+        --cluster-opt mesos.address=<public_machine_ip> \
+        --cluster-opt mesos.port=3375 \
+        zk://<mesos_masters_url>
 ```
 
-For example, if you run the manager locally on your machine:
+Once the manager is running, check your configuration by running `docker info`
+as follows:
 
 ```
+$ docker -H tcp://<swarm_ip>:<swarm_port> info
 Containers: 0
 Offers: 2
   Offer: 20150609-222929-1327399946-5050-14390-O6286
@@ -48,3 +67,7 @@ Offers: 2
      └ disk: 34.37 GiB
      └ ports: 31000-32000
 ```
+
+If you run into `Abnormal executor termination` error, you might want to run the
+swarm container with an additional environment variable:
+`SWARM_MESOS_USER=root`.