gh-122450: Expand numbers.Rational docstrings

Author: skirpichev

Lib/numbers.py

@@ -290,18 +290,24 @@ def conjugate(self):
 
 
 class Rational(Real):
-    """.numerator and .denominator should be in lowest terms."""
+    """To Real, adds numerator and denominator properties.
+
+    The numerator and denominator values should be in lowest terms with
+    denominator positive.
+    """
 
     __slots__ = ()
 
     @property
     @abstractmethod
     def numerator(self):
+        """The numerator of a rational number in lowest terms."""
         raise NotImplementedError
 
     @property
     @abstractmethod
     def denominator(self):
+        """The positive denominator of a rational number in lowest terms."""
         raise NotImplementedError
 
     # Concrete implementation of Real's conversion to float.