docs: Move SET_TEMPERATURE_FAN_TARGET to its own section in G-Codes.md

Signed-off-by: Kevin O'Connor <[email protected]>

docs/G-Codes.md

@@ -210,8 +210,6 @@ The following standard commands are supported:
   defaults to "display" (the primary display).
 - `SET_IDLE_TIMEOUT [TIMEOUT=<timeout>]`:  Allows the user to set the
   idle timeout (in seconds).
-- `SET_TEMPERATURE_FAN_TARGET temperature_fan=<temperature_fan_name> [target=<target_temperature>]`:
-  Sets the target temperature for a temperature_fan. If a target is not supplied, it is set to the specified temperature in the config file.
 - `RESTART`: This will cause the host software to reload its config
   and perform an internal reset. This command will not clear error
   state from the micro-controller (see FIRMWARE_RESTART) nor will it
@@ -614,3 +612,12 @@ been enabled:
     of SHAPER_TYPE_X and SHAPER_TYPE_Y parameters. See
     [example-extras.cfg](https://github.com/KevinOConnor/klipper/tree/master/config/example-extras.cfg)
     for more details on each of these parameters.
+
+## Temperature Fan Commands
+
+The following command is available when a "temperature_fan" config
+section is enabled:
+- `SET_TEMPERATURE_FAN_TARGET temperature_fan=<temperature_fan_name>
+  [target=<target_temperature>]`: Sets the target temperature for a
+  temperature_fan. If a target is not supplied, it is set to the
+  specified temperature in the config file.