Tweak a paragraph in the documentation

ephem/doc/date.rst

@@ -129,10 +129,12 @@ Datetime objects
   is why PyEphem exposes its own date type
   instead of returning Python ``datetime`` objects automatically.
 
-  Note that python ``datetime`` objects use local time by default.
-  PyEphem expects UTC ``datetime`` objects. ``datetime.now()`` will
-  give unexpected results. Use ``datetime.utcnow()`` instead:
-
+  Note that Python ``datetime`` objects use your local time by default,
+  whereas PyEphem expects time to be expressed in UTC.
+  This means that passing ``datetime.now()`` to PyEphem
+  will give unexpected results.
+  Instead, use the ``datetime.utcnow()`` constructor:
+
     >>> d = datetime.datetime.utcnow()
     >>> ephem.Date(d)
     2015/12/14 15:42:14