update note for write_data command on missing coefficient data.

wild-card character.  The "\*" is replaced with the current timestep

value.

.. note::

   The write-data command is not yet fully implemented in two

   respects.  First, most pair styles do not yet write their coefficient

   information into the data file.  This means you will need to specify

   that information in your input script that reads the data file, via

   the :doc:`pair_coeff <pair_coeff>` command.  Second, a few of the :doc:`atom styles <atom_style>` (body, ellipsoid, line, tri) that store

   auxiliary "bonus" information about aspherical particles, do not yet

   write the bonus info into the data file.  Both these functionalities

   will be added to the write_data command later.

.. admonition:: Data in Coeff sections

   The write_data command may not always write all coefficient settings

   to the corresponding Coeff sections of the data file.  This can have

   one of multiple reasons. 1) A few styles may be missing the code that

   would writes those sections (if you come across one, please notify

   the LAMMPS developers). 2) Some pair styles require a single pair_coeff

   statement and those are not compatible with data files. 3) and finally

   the default for write_data is to write a PairCoeff section, which has

   only entries for atom types i == j. The remaining coefficients would

   be inferred through the currently selected mixing rule.  If there has

   been a pair_coeff command with i != j, this setting would be lost.

   LAMMPS will detect this and print a warning message unless *pair ij*

   is appended to the write_data command.  This will request writing a

   PairIJCoeff section which has information for all pairs of atom types.

   In cases where the coefficient data in the data file is incomplete,

   you will need to re-specify that information in your input script

   that reads the data file.

Because a data file is in text format, if you use a data file written

out by this command to restart a simulation, the initial state of the