Added docs for getting documents

docs/getting_documents.rst

@@ -1,2 +1,73 @@
 Getting Documents
 =================
+
+Like indexing documents, there are several ways to 'get' document(s) from
+the Elasticsearch server using `elasticsearch-lua`_.
+
+Getting Single Document
+-----------------------
+
+To get a single document, provide **index**, **type** and **id** of the
+document.
+
+.. code-block:: lua
+
+  local res, status = client:get{
+    index = "my_index",
+    type = "my_type",
+    id = "my_id"
+  }
+
+Getting Multiple Documents
+--------------------------
+
+Elasticsearch supports getting multiple documents using a single request. It is
+advised to use this method in case you want to retrieve multiple documents. You
+need to pass an array of Lua tables to the MGET API. Each table represents
+details about one document and consists of three fields **_index**, **_type**
+and **_id**.
+
+.. code-block:: lua
+
+  local res, status = client:mget{
+    body = {
+      docs = {
+        -- First document
+        {
+          ["_index"] = "my_index1",
+          ["_type"] = "my_type1",
+          ["_id"] = "my_id1"
+        },
+        -- Second document
+        {
+          ["_index"] = "my_index2",
+          ["_type"] = "my_type2",
+          ["_id"] = "my_id2"
+        }
+      }
+    }
+  }
+
+In case every document has the same **index** or **type**, they can be specified
+separately instead of passing them in every document table.
+
+.. code-block:: lua
+
+  local res, status = client:mget{
+    index = "my_index",
+    type = "my_type",
+    body = {
+      docs = {
+        -- First document
+        {
+          ["_id"] = "my_id1"
+        },
+        -- Second document
+        {
+          ["_id"] = "my_id2"
+        }
+      }
+    }
+  }
+
+.. _elasticsearch-lua: https://github.com/DhavalKapil/elasticsearch-lua