doc: emphasize name should be unique

Documentation/clustering.md

@@ -148,7 +148,7 @@ If you bootstrap an etcd cluster using discovery service with more than the expe
 
 The URL you will use in this case will be `https://myetcd.local/v2/keys/discovery/6c007a14875d53d9bf0ef5a6fc0257c817f0fb83` and the etcd members will use the `https://myetcd.local/v2/keys/discovery/6c007a14875d53d9bf0ef5a6fc0257c817f0fb83` directory for registration as they start.
 
-Each member must have a different name flag specified. Or discovery will fail due to duplicated name.
+**Each member must have a different name flag specified. `Hostname` or `machine-id` can be a good choice. Or discovery will fail due to duplicated name.** 
 
 Now we start etcd with those relevant flags for each member:
 
@@ -200,7 +200,7 @@ ETCD_DISCOVERY=https://discovery.etcd.io/3e86b59982e49066c5d813af1c2e2579cbf573d
 -discovery https://discovery.etcd.io/3e86b59982e49066c5d813af1c2e2579cbf573de
 ```
 
-Each member must have a different name flag specified. Or discovery will fail due to duplicated name.
+**Each member must have a different name flag specified. `Hostname` or `machine-id` can be a good choice. Or discovery will fail due to duplicated name.** 
 
 Now we start etcd with those relevant flags for each member:
 

Documentation/configuration.md

@@ -14,7 +14,7 @@ To start etcd automatically using custom settings at startup in Linux, using a [
 + Human-readable name for this member.
 + default: "default"
 + env variable: ETCD_NAME
-+ This value is referenced as this node's own entries listed in the `-initial-cluster` flag (Ex: `default=http://localhost:2380` or `default=http://localhost:2380,default=http://localhost:7001`). This needs to match the key used in the flag if you're using [static bootstrapping](clustering.md#static).
++ This value is referenced as this node's own entries listed in the `-initial-cluster` flag (Ex: `default=http://localhost:2380` or `default=http://localhost:2380,default=http://localhost:7001`). This needs to match the key used in the flag if you're using [static bootstrapping](clustering.md#static). When using discovery, each member must have a unique name. `Hostname` or `machine-id` can be a good choice.
 
 ##### -data-dir
 + Path to the data directory.