Documentation: bindings: fix twl-rtc documentation

Add interrupts documentation
Fix example and formatting
Signed-off-by: NNicolae Rosia <Nicolae_Rosia@mentor.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/devicetree/bindings/rtc/twl-rtc.txt

-* TI twl RTC
-
-The TWL family (twl4030/6030) contains a RTC.
+* Texas Instruments TWL4030/6030 RTC
 
 Required properties:
-- compatible : Should be twl4030-rtc
-
-Examples:
+- compatible : Should be "ti,twl4030-rtc"
+- interrupts : Should be the interrupt number.
 
-rtc@0 {
+Example:
+	rtc {
 		compatible = "ti,twl4030-rtc";
-};
+		interrupts = <11>;
+	};