Add documentation for number in the Flexit Nordic integration (#31367)

* Add documentation for number in the Flexit Nordic integration

* tiny tweak

---------

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_integrations/flexit_bacnet.markdown

@@ -9,6 +9,7 @@ ha_domain: flexit_bacnet
 ha_platforms:
   - binary_sensor
   - climate
+  - number
   - sensor
   - switch
 ha_integration_type: device
@@ -63,6 +64,16 @@ The integration adds entities for sensors with different readings from the devic
 
 The integration adds an entity for a binary sensor called _Air filter polluted_ which tells if it's time to change the filters in the unit.
 
+### Number
+
+The integration adds entities for setting setpoints for the fan in the respective mode:
+
+ - Away
+ - Home
+ - Fireplace
+ - High
+ - Cooker hood
+
 ### Switch
 
 The integration adds an entity for a switch called _Electric heater_ that controls the heating element in the unit.