DOCS-1049 add projection argument in findOne method ref

Author: kay-kim

source/reference/method/db.collection.find.txt

@@ -42,11 +42,17 @@ db.collection.find()
 
           The ``projection`` cannot contain both include and exclude
           specifications except for the exclusion of the ``_id`` field.
+          
+          Omit the ``projection`` parameter to return **all** the fields in
+          the matching documents.
 
    :returns:
 
-      A :term:`cursor` to the documents that match
-      the ``query`` criteria and contain the ``projection`` fields.
+      A :term:`cursor` to the documents that match the ``query``
+      criteria. If the ``projection`` argument is specified, the
+      matching documents contain only the ``projection`` fields, and
+      the ``_id`` field if you do not explicitly exclude the ``_id``
+      field.
 
    .. note::
 

source/reference/method/db.collection.findOne.txt

@@ -4,14 +4,42 @@ db.collection.findOne()
 
 .. default-domain:: mongodb
 
-.. method:: db.collection.findOne(query)
+.. method:: db.collection.findOne(query,projection)
 
    :param document query: Optional. A :term:`document` that specifies the :term:`query`
                           using the JSON-like syntax and :doc:`query operators
                           </reference/operators>`.
+   :param document projection:
+
+          Optional. Controls the fields to return, or the
+          :term:`projection`. The ``projection`` argument will
+          resemble the following prototype:
+
+          .. code-block:: javascript
+
+              { field1: boolean, field2: boolean ... }
+
+          The ``boolean`` can take the following include or exclude
+          values:
+
+          - ``1`` or ``true`` to include. The
+            :method:`~db.collection.findOne()` method always includes
+            the :term:`_id` field even if the field is not explicitly
+            stated to return in the :term:`projection` parameter.
+
+          - ``0`` or ``false`` to exclude.
+
+          The ``projection`` cannot contain both include and exclude
+          specifications except for the exclusion of the ``_id`` field.
+
+          Omit the ``projection`` parameter to return **all** the fields in
+          the matching documents.
 
    :returns: One document that satisfies the query specified as the
-             argument to this method.
+             argument to this method. If the ``projection`` argument is
+             specified, the returned document contains only the
+             ``projection`` fields, and the ``_id`` field if you do not
+             explicitly exclude the ``_id`` field.
 
    Returns only one document that satisfies the specified query. If
    multiple documents satisfy the query, this method returns the first