minor: stylistic changes to unwind aggregation reference

Author: Sam Kleinman

source/reference/aggregation.txt

@@ -395,24 +395,25 @@ The current pipeline operators are:
 
    .. note::
 
-      The following behaviors are present in :pipeline:`$unwind`:
+      :pipeline:`$unwind` has the following behaviors:
 
       - :pipeline:`$unwind` is most useful in combination
         with :pipeline:`$group`.
 
-      - The effects of an unwind can be undone with the
-        :pipeline:`$group` pipeline operators.
+      - You may undo the effects of unwind operation with the
+        :pipeline:`$group` pipeline operator.
 
       - If you specify a target field for :pipeline:`$unwind` that
-        does not exist in an input document, the input document is
-        ignored (generates no result documents).
+        does not exist in an input document, the pipeline ignores the
+        input document, and will generates no result documents.
 
       - If you specify a target field for :pipeline:`$unwind` that is
         not an array, :mongodb:func:`aggregate()` generates an error.
 
       - If you specify a target field for :pipeline:`$unwind` that
-        holds an empty array (``[]``) in an input document, the input
-        document is ignored (generates no result documents).
+        holds an empty array (``[]``) in an input document, the
+        pipeline ignores the input document, and will generates no
+        result documents.
 
 .. pipeline:: $group