[DOCS] Change index name in rollover ILM example
The warning section above the example tells that index name has to end with the digits but the example itself uses index name without digits which is confusing.
@@ -361,12 +361,12 @@ follower index into a regular index as if <<ilm-unfollow-action,the Unfollow
action>> had been used instead of rolling over.
For example, if an index to be managed has an alias `my_data`. The managed
-index "my_index" must be the write index for the alias. For more information, read
+index "my_index-000001" must be the write index for the alias. For more information, read
<<indices-rollover-is-write-index,Write Index Alias Behavior>>.
[source,js]
--------------------------------------------------
-PUT my_index
+PUT my_index-000001
{
"settings": {
"index.lifecycle.name": "my_policy",
