Update Range.int-bounds doc

Reflects the tightened implementation.

Author: lizmat

doc/Type/Range.pod6

@@ -245,7 +245,7 @@ Returns C<True> if both end points are C<Int> values.
 
     proto method int-bounds(|)
     multi method int-bounds()
-    multi method int-bounds($from is rw, $to is rw)
+    multi method int-bounds($from is rw, $to is rw --> Bool:D)
 
 If the C<Range> is an integer range (as indicated by L<is-int|/routine/is-int>), then this
 method returns a list with the first and last value it will iterate over
@@ -256,11 +256,15 @@ Failure if it is not an integer range.
     say (2..^5).int-bounds;                           # OUTPUT: «(2 4)␤»
 
 If called with (writable) arguments, these will take the the values of the
-higher and lower bound:
-
-    (3..5).int-bounds( my $min, my $max);
-    say "$min, $max" ; # OUTPUT: «3, 5␤»
-
+higher and lower bound and returns whether integer bounds could be determined
+from the C<Range>:
+
+    if (3..5).int-bounds( my $min, my $max) {
+        say "$min, $max" ; # OUTPUT: «3, 5␤»
+    }
+    else {
+        say "Could not determine integer bounds";
+    }
 
 =head2 method minmax