Add more documentation and examples about dlt operator (#42)

* Add more documentation and examples about `dlt` operator

* add dlt docs to swagger

README.md

@@ -318,7 +318,8 @@ A `filter` has the form `alias.operator.value_or_list`.
   covered by the box)
 - `bbc`: Bounding box containing objects (e.g. a station or street, that is
   completely covered by the box)
-- `dlt`: Within distance from point (e.g. all stations within a 5 km radius from point X)
+- `dlt`: Within distance from point (e.g. all stations within a 5 km radius from point X)   
+    [Learn more and see examples.](https://github.com/noi-techpark/odh-docs/wiki/Time-series-API-filter-operators#dlt-operator)
 - `in`: True, if the value of the alias can be found within the given list.
   Example: `name.in.(Patrick,Rudi,Peter)`
 - `nin`: False, if the value of the alias can be found within the given list.

src/main/resources/openapi3.yml

@@ -649,7 +649,7 @@ components:
          -   nire: Negated Insensitive Regular Expression
          -   bbi: Bounding box intersecting objects (ex., a street that is only partially covered by the box). Syntax? See below.
          -   bbc: Bounding box containing objects (ex., a station or street, that is completely covered by the box). Syntax? See below.
-         -   dlt: Within distance (in meters) from point. Syntax? See below.
+         -   dlt: Within distance (in meters) from point. [Learn more and see examples](https://github.com/noi-techpark/odh-docs/wiki/Time-series-API-filter-operators#dlt-operator)
          -   in: True, if the value of the alias can be found within the given list. Example: name.in.(Peter,Patrick,Rudi)
          -   nin: False, if the value of the alias can be found within the given list. Example: name.nin.(Peter,Patrick,Rudi)