[DOCS] Document `indices.recovery.concurrent_small_file_streams`

docs/reference/cluster/update-settings.asciidoc

@@ -168,6 +168,9 @@ due to forced awareness or allocation filtering.
 `indices.recovery.concurrent_streams`::
      See <<modules-indices>>
 
+`indices.recovery.concurrent_small_file_streams`::
+     See <<modules-indices>>
+
 `indices.recovery.file_chunk_size`::
      See <<modules-indices>>
 

docs/reference/modules/cluster.asciidoc

@@ -73,6 +73,10 @@ Can be set to:
        The number of streams to open (on a *node* level) to recover a
        shard from a peer shard. Defaults to `3`.
 
+`indices.recovery.concurrent_small_file_streams`::
+       The number of streams to open (on a *node* level) for small files (under
+       5mb) to recover a shard from a peer shard. Defaults to `2`.
+
 [float]
 [[allocation-awareness]]
 === Shard Allocation Awareness

docs/reference/modules/indices.asciidoc

@@ -46,6 +46,9 @@ The following settings can be set to manage the recovery policy:
 `indices.recovery.concurrent_streams`::
     defaults to `3`.
 
+`indices.recovery.concurrent_small_file_streams`::
+    defaults to `2`.
+
 `indices.recovery.file_chunk_size`::
     defaults to `512kb`.