Minor improvement to the sleep-until function.

Source code from moar2018.01.

Author: fluca1978

doc/Type/Date.pod6

@@ -271,11 +271,16 @@ say sleep-timer 0;  # OUTPUT: 0
 
     sub sleep-until(Instant $until --> Bool)
 
-Works just like C<sleep> but checks the current time and goes back to sleep
-if accidentally woken up early, to guarantee waiting until the specified
-time.  Returns C<True> if the function actually waited, or if the specified
-time happens to be the present moment.  Returns C<False> if you asked to
-sleep until a time in the past.
+Works similar to C<sleep> but checks the current time and keeps sleeping
+until the required instant in the future has been reached.
+It uses internally the C<sleep-timer> method in a loop to ensure that,
+if accidentaly woken up early, it will wait again for the specified
+amount of time remaining to reach the specified instant.
+goes back to sleep
+
+Returns C<True> if the C<Instant> in the future has been achieved (either
+by mean of sleeping or because it is right now), C<False> in the case
+an C<Instant> in the past has been specified.
 
 To sleep until 10 seconds into the future, one could write something like this: