Add term filter doc.

docs/Filter/Term.md

+# Term Filter
+
+> More info about term filter is in the [official elasticsearch docs][1]
+
+Filters documents that have fields that contain a term.
+
+## Simple example
+
+```JSON
+{
+    "filter" : {
+        "term" : { "user" : "kimchy"}
+    }
+}
+```
+
+And now the query via DSL:
+
+```php
+$termFilter = new TermFilter('user', 'kimchy');
+
+$search = new Search();
+$search->addFilter($termFilter);
+
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-term-filter.html