Add documentation for Java API update/get settings API

Closes #10941.

docs/java-api/admin/indices/get-settings.asciidoc

@@ -0,0 +1,22 @@
+[[java-admin-indices-get-settings]]
+==== Get Settings
+
+The get settings API allows to retrieve settings of index/indices:
+
+[source,java]
+--------------------------------------------------
+GetSettingsResponse response = client.admin().indices()
+        .prepareGetSettings("company", "employee").get();                           <1>
+for (ObjectObjectCursor<String, Settings> cursor : response.getIndexToSettings()) { <2>
+    String index = cursor.key;                                                      <3>
+    Settings settings = cursor.value;                                               <4>
+    Integer shards = settings.getAsInt("index.number_of_shards", null);             <5>
+    Integer replicas = settings.getAsInt("index.number_of_replicas", null);         <6>
+}
+--------------------------------------------------
+<1> Get settings for indices `company` and `employee`
+<2> Iterate over results
+<3> Index name
+<4> Settings for the given index
+<5> Number of shards for this index
+<6> Number of replicas for this index

docs/java-api/admin/indices/index.asciidoc

@@ -14,3 +14,6 @@ In the rest of this guide, we will use `client.admin().indices()`.
 include::create-index.asciidoc[]
 
 include::put-mapping.asciidoc[]
+
+include::get-settings.asciidoc[]
+include::update-settings.asciidoc[]

docs/java-api/admin/indices/update-settings.asciidoc

@@ -0,0 +1,16 @@
+[[java-admin-indices-update-settings]]
+==== Update Indices Settings
+
+You can change index settings by calling:
+
+[source,java]
+--------------------------------------------------
+client.admin().indices().prepareUpdateSettings("twitter")   <1>
+        .setSettings(Settings.builder()                     <2>
+                .put("index.number_of_replicas", 0)
+        )
+        .get();
+--------------------------------------------------
+<1> Index to update
+<2> Settings
+