Document supported platforms for `Input.get_accelerometer()` and related

This closes #41303.

doc/classes/Input.xml

@@ -47,8 +47,9 @@
 			<return type="Vector3">
 			</return>
 			<description>
-				If the device has an accelerometer, this will return the acceleration. Otherwise, it returns an empty [Vector3].
+				Returns the acceleration of the device's accelerometer, if the device has one. Otherwise, the method returns [constant Vector3.ZERO].
 				Note this method returns an empty [Vector3] when running from the editor even when your device has an accelerometer. You must export your project to a supported device to read values from the accelerometer.
+				[b]Note:[/b] This method only works on iOS, Android, and UWP. On other platforms, it always returns [constant Vector3.ZERO].
 			</description>
 		</method>
 		<method name="get_action_strength" qualifiers="const">
@@ -78,14 +79,16 @@
 			<return type="Vector3">
 			</return>
 			<description>
-				If the device has an accelerometer, this will return the gravity. Otherwise, it returns an empty [Vector3].
+				Returns the gravity of the device's accelerometer, if the device has one. Otherwise, the method returns [constant Vector3.ZERO].
+				[b]Note:[/b] This method only works on Android and iOS. On other platforms, it always returns [constant Vector3.ZERO].
 			</description>
 		</method>
 		<method name="get_gyroscope" qualifiers="const">
 			<return type="Vector3">
 			</return>
 			<description>
-				If the device has a gyroscope, this will return the rate of rotation in rad/s around a device's X, Y, and Z axes. Otherwise, it returns an empty [Vector3].
+				Returns the rotation rate in rad/s around a device's X, Y, and Z axes of the gyroscope, if the device has one. Otherwise, the method returns [constant Vector3.ZERO].
+				[b]Note:[/b] This method only works on Android. On other platforms, it always returns [constant Vector3.ZERO].
 			</description>
 		</method>
 		<method name="get_joy_axis" qualifiers="const">
@@ -182,7 +185,8 @@
 			<return type="Vector3">
 			</return>
 			<description>
-				If the device has a magnetometer, this will return the magnetic field strength in micro-Tesla for all axes.
+				Returns the the magnetic field strength in micro-Tesla for all axes of the device's magnetometer, if the device has one. Otherwise, the method returns [constant Vector3.ZERO].
+				[b]Note:[/b] This method only works on Android and UWP. On other platforms, it always returns [constant Vector3.ZERO].
 			</description>
 		</method>
 		<method name="get_mouse_button_mask" qualifiers="const">