Updated README to define pps-rp1.

Signed-off-by: Josh Blake <mail@josh.to>

Author: josh-blake

arch/arm/boot/dts/overlays/README

@@ -4152,6 +4152,46 @@ Params: gpiopin                 Input GPIO (default "18")
                                 Default is "off".
 
 
+Name:   pps-rp1
+
+Info:   Configures the pps-gpio kernel module for use with the RP1 found on the
+	RPi 5 (pulse-per-second time signal via GPIO).
+
+Load:   dtoverlay=pps-rp1,<param>=<val>
+
+Params:	pin			(integer) Specifies the PPS Input pin.
+				Takes the pin number correlating to the RPi 40-pin GPIO Header.
+				Defaults to GPIO 18.
+
+	pull-none		(boolean) Disable pull-up/down resistors on the PPS Input pin.
+
+	pull-up			(boolean) Enable pull-up resistor on the PPS Input pin.
+
+	pull-down		(boolean) Enable pull-down resistor on the PPS Input pin.
+
+	schmitt-trigger		(boolean) Enable the Schmitt-trigger on the PPS Input pin.
+				Defaults to off.
+
+	echo-pin		(integer) Specifies the PPS Echo Output pin.
+				Takes the pin number correlating to the RPi 40-pin GPIO Header.
+				Defaults to GPIO 17.
+
+	echo-ms			(integer) Specifies the pulse-width in ms that the echo signal
+				outputs on the PPS Echo Output pin.
+				Must be less than 999.
+				Defaults to 10ms.
+
+	echo			(boolean) Enables the PPS Echo Output signal.
+				Defaults to off.
+
+	capture-clear		(boolean) Captures the clear event time.
+				Defaults to off.
+
+	assert-falling-edge	(boolean) Uses the falling signal edge instead of the
+				rising signal edge.
+				Defaults to off.
+
+
 Name:   proto-codec
 Info:   Configures the PROTO Audio Codec card
 Load:   dtoverlay=proto-codec