DOCSP-40654-sample-aggregation-operator (mongodb#360)

* DOCSP-40654-sample-aggregation-operator

* changed some syntax

* update code example

Author: gmiller-mdb

source/fundamentals/linq.txt

@@ -249,6 +249,32 @@ The result of the preceding example contains the following documents:
     { "name" : "Crystal Room", "cuisine" : "Italian" }
     { "name" : "Forlinis Restaurant", "cuisine" : "Italian" }
 
+$sample
+~~~~~~~
+
+The ``$sample`` aggregation stage returns a random sample of documents from a 
+collection. The following example shows how to generate a ``$sample`` stage by using
+LINQ: 
+
+.. code-block:: csharp
+   :emphasize-lines: 4
+
+   var query = queryableCollection
+       .Aggregate()
+       .Sample(4)
+       .ToList();
+
+The result of the preceding example contains the following documents:
+
+.. code-block:: json
+
+   // Results Truncated
+
+   { "name" : "Von Dolhens", "cuisine" : "Ice Cream, Gelato, Yogurt, Ices" }
+   { "name" : "New York Mercantile Exchange", "cuisine" : "American" }
+   { "name" : "Michaelangelo's Restaurant", "cuisine" : "Italian" }
+   { "name" : "Charlie Palmer Steak", "cuisine" : "American" }
+
 $skip
 ~~~~~