Document Rational.floor/.ceiling

They differ from Real's in that they can `fail`
POV for failing: rakudo/rakudo@6d70346cbf
Propspec for failing: Raku/roast@17761c2e48

Author: zoffixznet

doc/Type/Rational.pod6

@@ -56,6 +56,24 @@ If L<denominator> is C<0>, returns C<Inf>, C<-Inf>, or C<NaN>, based on
 whether L<numerator> is a positive number, negative number, or C<0>,
 respectively.
 
+=head2 method ceiling
+
+Defined as:
+
+    method ceiling(Rational:D: --> Int:D)
+
+Return the smallest integer not greater than the invocant. If L<denominator>
+is zero, L<fails|/routine/fail> with C<X::Numeric::DivideByZero>.
+
+=head2 method floor
+
+Defined as:
+
+    method floor(Rational:D: --> Int:D)
+
+Return the largest integer not greater than the invocant. If L<denominator>
+is zero, L<fails|/routine/fail> with C<X::Numeric::DivideByZero>.
+
 =head2 method isNaN
 
 =for code