DOC: enhance documentation for date_range

Added extended summary.

Author: plammens

pandas/core/indexes/datetimes.py

@@ -864,6 +864,15 @@ def date_range(
     """
     Return a fixed frequency DatetimeIndex.
 
+    Returns the range of equally spaced timesteps (where the time offset between any
+    two adjacent timesteps is specified by the given frequency) such that they all
+    satisfy `start <[=] timestep <[=] end`, where the first and last timesteps are
+    the first and last timesteps in that range that fall on the boundary of ``freq``
+    (if given as a frequency string) or that are valid for ``freq`` (if given as a
+    :class:`pandas.tseries.offsets.DateOffset`). (If exactly one of ``start``,
+    ``end``, or ``freq`` is not specified, it can be computed given ``periods``,
+    the number of timesteps in the range. See the note below.)
+
     Parameters
     ----------
     start : str or datetime-like, optional