Doc: clarify that Servo::read() only reads the setpoint

“The current angle of the servo” could be misunderstood as its physical
orientation.

Author: edgar-bonet

docs/api.md

@@ -118,7 +118,9 @@ void loop() {}
 
 ### `read()`
 
-Read the current angle of the servo (the value passed to the last call to [write()](#write)).
+Read the current setpoint of the servo (the angle passed to the last call to [write()](#write)).
+
+Note that the servo has no way of reporting its current physical orientation. This method returns the angle that has been requested to the servo, whether this angle has already been reached or not.
 
 #### Syntax
 
@@ -132,7 +134,7 @@ servo.read()
 
 #### Returns
 
-The angle of the servo, from 0 to 180 degrees.
+The setpoint of the servo, as an angle from 0 to 180 degrees.
 
 #### See also