Add select and button to REST API docs (#1805)

web-api/index.rst

@@ -249,3 +249,29 @@ can be used:
 Creating a POST request to ``/cover/front_window_blinds/set?position=0.1&tilt=0.3`` will
 start moving the blinds towards an almost completely closed position and a new tilt
 angle.
+
+Select
+******
+
+Selects can be set to an option and will return their current option. For example sending
+a GET request to ``/select/house_mode`` could yield this payload:
+
+.. code-block:: json
+
+    {
+      "id": "select-house_mode",
+      "state": "party",
+      "value": "party"
+    }
+
+POST requests on the other hand allow setting the select, the available
+method is ``set``. The following parameter can be used:
+
+-  **option**: The string option to set it to. Must be a valid option.
+
+For example POST ``/select/house_mode/set?option=guest`` will set the select to ``guest``.
+
+Button
+******
+
+A button can be ``pressed`` from the REST API by sending a POST request to ``button/do_something/press``.