A tad of aggregation documentation

Author: andersosthus

docs/contents/nest/aggregations/advanced.markdown

@@ -0,0 +1,39 @@
+---
+template: layout.jade
+title: Aggregations
+menusection: aggregations
+menuitem: advanced
+---
+
+# Advanced usage
+
+## Creating multiple aggregations from an IEnumerable
+
+Premise:
+You have an IEnumerable<TestObject> MyFilters, and you want to build a Filter aggregation with a Term filter for each of the TestObjects you have.
+
+	class TestObject
+	{
+		public string Name { get; set; }
+		public string Term { get; set; }
+	}
+
+Then you could do something like this:
+
+	var descriptor = new SearchDescriptor<MySearchType>().Query(q => q.MatchAll());
+
+	descriptor.Aggregations(aggr => 
+	{
+		foreach (var term in MyFilters)
+		{
+			aggr.Filter(term.Name, filter => filter
+				.Filter(f => f
+					.Term("TheTermField", term.Term)))
+		}
+
+		return aggr;
+	});
+
+	var result = client.Search<MySearchType>(descriptor);
+
+And then you can access the aggregation results as normal.