added documentation for geo polygon query (#219)

docs/Query/Geo/GeoPolygon.md

-Documentation in progress...
\ No newline at end of file
+# Geo Polygon Query
+
+> More info about geo polygon query is in the [official elasticsearch docs][1]
+
+A query allowing to include hits that only fall within a polygon of points. Here is an example:
+
+## Simple example
+
+```JSON
+{
+    "query": {
+        "bool" : {
+            "must" : {
+                "match_all" : {}
+            },
+            "filter" : {
+                "geo_polygon" : {
+                    "person.location" : {
+                        "points" : [
+                        {"lat" : 40, "lon" : -70},
+                        {"lat" : 30, "lon" : -80},
+                        {"lat" : 20, "lon" : -90}
+                        ]
+                    }
+                }
+            }
+        }
+    }
+}
+```
+
+In DSL:
+
+```php
+$points = [
+    ['lat' => 40, 'lon' => -70],
+    ['lat' => 30, 'lon' => -80],
+    ['lat' => 20, 'lon' => -90],
+];
+$search = new Search();
+$boolQuery = new BoolQuery();
+$boolQuery->add(new MatchAllQuery());
+$geoQuery = new GeoPolygonQuery('person.location', $points);
+$boolQuery->add($geoQuery, BoolQuery::FILTER);
+$search->addQuery($boolQuery);
+
+$queryArray = $search->toArray();
+```
+
+[1]: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-geo-polygon-query.html