Merge pull request #5648 from ingvagabund/doc-nits

docs: Clustering.md: Switch "command line" and "environment variables"

Documentation/op-guide/clustering.md

@@ -22,7 +22,7 @@ Each of the bootstrapping mechanisms will be used to create a three machine etcd
 
 ## Static
 
-As we know the cluster members, their addresses and the size of the cluster before starting, we can use an offline bootstrap configuration by setting the `initial-cluster` flag. Each machine will get either the following command line or environment variables:
+As we know the cluster members, their addresses and the size of the cluster before starting, we can use an offline bootstrap configuration by setting the `initial-cluster` flag. Each machine will get either the following environment variables or command line:
 
 ```
 ETCD_INITIAL_CLUSTER="infra0=http://10.0.1.10:2380,infra1=http://10.0.1.11:2380,infra2=http://10.0.1.12:2380"