Add skin to pair_kim neigh-list cutoffs & update docs

instructions on how to do this with a simple make command, when

building LAMMPS.

See the examples/kim dir for an input script that uses a KIM model

(potential) for Lennard-Jones.

See the examples/kim dir for an input script that uses a KIM model (potential)

for Lennard-Jones.  Note, for this example input script, the example models

shipped with with kim-api package must be installed.  See the "Making

LAMMPS"_Section_start.html#start_3 section and the ./lib/kim/README for details

on how to build LAMMSPS with the kim-api and how to install the example models.

:line

# 3d Lennard-Jones melt

#

# This example requires that the example models provided with

# the kim-api package are installed.  see the ./lib/kim/README or

# ./lib/kim/Install.py files for details on how to install these

# example models.

#

variable	x index 1

variable	y index 1

$ make

$ make install

$ cd ..

4. Remove source and build files

4. To install the example models shipped with the kim-api

$ cd examples

$ make model-drivers-all-system

$ make models-all-system

$ cd ../..

5. Remove source and build files

$ rm -rf kim-api-vX.Y.Z

$ rm -rf kim-api-vX.Y.Z.txz

5. To add items do the following (replace the kim item name with your

6. To add items do the following (replace the kim item name with your

   desired value)

$ source ${PWD}/kim-api-vX.Y.Z/bin/kim-api-vX-activate

     neighbor->requests[irequest]->full = 1;

     neighbor->requests[irequest]->ghost = 1;

     neighbor->requests[irequest]->cut = 1;

     neighbor->requests[irequest]->cutoff = kim_cutoff_values[i];

     neighbor->requests[irequest]->cutoff

         = kim_cutoff_values[i] + neighbor->skin;

   }

   return;