Added brief discussion on how to use presets files with CMake

doc/src/Build_package.txt

@@ -130,9 +130,35 @@ the Git or SVN repositories, no packages are pre-installed.
 
 [CMake shortcuts for installing many packages]:
 
-TODO: brief discussion of the cmake command line options with presets
-that Axel or Richard enabled to install sets of packages at once?
-Are these just for cmake, or also ccmake and cmake-gui?
+Instead of specifying all the CMake options via the command-line, CMake allows
+initializing the variable cache using script files. These are regular CMake
+files which can manipulate and set variables, and can also contain control flow
+constructs.
+
+LAMMPS includes several of these files to define configuration "presets",
+similar to the options that exist for the Make based system. Using these files
+you can enable/disable portions of the available packages in LAMMPS. If you need a
+custom preset you can take one of them as a starting point and customize it to your
+needs.
+
+cmake -C ../cmake/presets/all_on.cmake \[OPTIONS\] ../cmake | enable all packages
+cmake -C ../cmake/presets/all_off.cmake \[OPTIONS\] ../cmake | disable all packages
+cmake -C ../cmake/presets/std.cmake \[OPTIONS\] ../cmake | enable standard packages
+cmake -C ../cmake/presets/user.cmake \[OPTIONS\] ../cmake | enable user packages
+cmake -C ../cmake/presets/std_nolib.cmake \[OPTIONS\] ../cmake | enable standard packages that do not require extra libraries
+cmake -C ../cmake/presets/nolib.cmake \[OPTIONS\] ../cmake | disable all packages that do not require extra libraries
+cmake -C ../cmake/presets/manual_selection.cmake \[OPTIONS\] ../cmake | example of how to create a manual selection of packages :tb(s=|,a=l)
+
+NOTE: Running cmake this way manipulates the variable cache in your current
+build directory. You can combine presets and options with multiple cmake runs.
+
+[Example:]
+
+# build LAMMPS with all "standard" packages which don't
+# use libraries and enable GPU package
+mkdir build
+cd build
+cmake -C ../cmake/presets/std_nolib.cmake -D PKG_GPU=on ../cmake :pre
 
 :line