adc_temperature: Add builtin definition for PT1000 sensors

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/example-extras.cfg

@@ -874,6 +874,19 @@
 #voltage_offset: 0
 #   The ADC voltage offset (in Volts). The default is 0.
 
+# Directly connected PT1000 sensor. The following parameters are
+# available in heater sections that use one of these sensors.
+#[extruder]
+# See the "extruder" section in example.cfg for a description of
+# heater parameters. The parameters below describe sensor parameters.
+#sensor_type: PT1000
+#sensor_pin:
+#   Analog input pin connected to the sensor. This parameter must be
+#   provided.
+#pullup_resistor: 4700
+#   The resistance (in ohms) of the pullup attached to the sensor. The
+#   default is 4700 ohms.
+
 # Custom thermistors (one may define any number of sections with a
 # "thermistor" prefix). A custom thermistor may be used in the
 # sensor_type field of a heater config section. (For example, if one