updating the Build_extras, KIM package

To build with this package, the KIM library with API v2 must be downloaded

and built on your system. It must include the KIM models that you want to

use with LAMMPS. If you want to use the :doc:`kim_query <kim_commands>`

use with LAMMPS.

If you would like to use the :doc:`kim_query <kim_commands>`

command, you also need to have libcurl installed with the matching

development headers and the curl-config tool.

See the `Obtaining KIM Models <http://openkim.org/doc/usage/obtaining-models>`_

web page to

If you would like to use the :doc:`kim_property <kim_commands>`

command, you need to build LAMMPS with the Python 3.6 or later package

installed. See the :doc:`Python <python>` doc page for more info on building

LAMMPS with the version of Python on your system.

After successfully building LAMMPS with Python, you need to

install the kim-property Python package, which can be easily done using

*pip* as ``pip install kim-property``, or from the *conda-forge* channel as

``conda install kim-property`` if LAMMPS is built in Conda. More detailed

information is available at:

`kim-property installation <https://github.com/openkim/kim-property#installing-kim-property>`_.

In addition to installing the KIM API, it is also necessary to install the

library of KIM models (interatomic potentials).

See `Obtaining KIM Models <http://openkim.org/doc/usage/obtaining-models>`_ to

learn how to install a pre-build binary of the OpenKIM Repository of Models.

See the list of all KIM models here: https://openkim.org/browse/models