[DOCS] Added multi-index open/close

docs/reference/indices/open-close.asciidoc

@@ -16,3 +16,13 @@ curl -XPOST 'localhost:9200/my_index/_close'
 
 curl -XPOST 'localhost:9200/my_index/_open'
 --------------------------------------------------
+
+It is possible to open and close multiple indices. An error will be thrown
+if the request explicitly refers to a missing index. This behaviour can be
+disabled using the `ignore_indices=missing` parameter.
+
+All indices can be opened or closed at once using `_all` as the index name
+or specifying patterns that identify them all (e.g. `*`).
+Closing all indices can be disabled by setting the `action.disable_close_all_indices`
+flag in the config file to `true`.
+