cpupower: Improve cpupower build process description

Enhance cpupower build process description with the information on
building and installing the utility to the user defined directories
as well as with the information on the way of running the utility from
the custom defined installation directory.

Signed-off-by: Roman Storozhenko <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/power/cpupower/README

···
 compilation and installation
 ----------------------------
 
-make
-su
-make install
+There are 2 output directories - one for the build output and another for
+the installation of the build results, that is the utility, library,
+man pages, etc...
 
-should suffice on most systems. It builds libcpupower to put in
-/usr/lib; cpupower, cpufreq-bench_plot.sh to put in /usr/bin; and
-cpufreq-bench to put in /usr/sbin. If you want to set up the paths
-differently and/or want to configure the package to your specific
-needs, you need to open "Makefile" with an editor of your choice and
-edit the block marked CONFIGURATION.
+default directory
+-----------------
+
+In the case of default directory, build and install process requires no
+additional parameters:
+
+build
+-----
+
+$ make
+
+The output directory for the 'make' command is the current directory and
+its subdirs in the kernel tree:
+tools/power/cpupower
+
+install
+-------
+
+$ sudo make install
+
+'make install' command puts targets to default system dirs:
+
+-----------------------------------------------------------------------
+| Installing file        |               System dir                   |
+-----------------------------------------------------------------------
+| libcpupower            | /usr/lib                                   |
+-----------------------------------------------------------------------
+| cpupower               | /usr/bin                                   |
+-----------------------------------------------------------------------
+| cpufreq-bench_plot.sh  | /usr/bin                                   |
+-----------------------------------------------------------------------
+| man pages              | /usr/man                                   |
+-----------------------------------------------------------------------
+
+To put it in other words it makes build results available system-wide,
+enabling any user to simply start using it without any additional steps
+
+custom directory
+----------------
+
+There are 2 make's command-line variables 'O' and 'DESTDIR' that setup
+appropriate dirs:
+'O' - build directory
+'DESTDIR' - installation directory. This variable could also be setup in
+the 'CONFIGURATION' block of the "Makefile"
+
+build
+-----
+
+$ make O=<your_custom_build_catalog>
+
+Example:
+$ make O=/home/hedin/prj/cpupower/build
+
+install
+-------
+
+$ make O=<your_custom_build_catalog> DESTDIR=<your_custom_install_catalog>
+
+Example:
+$ make O=/home/hedin/prj/cpupower/build DESTDIR=/home/hedin/prj/cpupower \
+> install
+
+Notice that both variables 'O' and 'DESTDIR' have been provided. The reason
+is that the build results are saved in the custom output dir defined by 'O'
+variable. So, this dir is the source for the installation step. If only
+'DESTDIR' were provided then the 'install' target would assume that the
+build directory is the current one, build everything there and install
+from the current dir.
+
+The files will be installed to the following dirs:
+
+-----------------------------------------------------------------------
+| Installing file        |               System dir                   |
+-----------------------------------------------------------------------
+| libcpupower            | ${DESTDIR}/usr/lib                         |
+-----------------------------------------------------------------------
+| cpupower               | ${DESTDIR}/usr/bin                         |
+-----------------------------------------------------------------------
+| cpufreq-bench_plot.sh  | ${DESTDIR}/usr/bin                         |
+-----------------------------------------------------------------------
+| man pages              | ${DESTDIR}/usr/man                         |
+-----------------------------------------------------------------------
+
+If you look at the table for the default 'make' output dirs you will
+notice that the only difference with the non-default case is the
+${DESTDIR} prefix. So, the structure of the output dirs remains the same
+regardles of the root output directory.
+
+
+clean and uninstall
+-------------------
+
+'clean' target is intended for cleanup the build catalog from build results
+'uninstall' target is intended for removing installed files from the
+installation directory
+
+default directory
+-----------------
+
+This case is a straightforward one:
+$ make clean
+$ make uninstall
+
+custom directory
+----------------
+
+Use 'O' command line variable to remove previously built files from the
+build dir:
+$ make O=<your_custom_build_catalog> clean
+
+Example:
+$ make O=/home/hedin/prj/cpupower/build clean
+
+Use 'DESTDIR' command line variable to uninstall previously installed files
+from the given dir:
+$ make DESTDIR=<your_custom_install_catalog>
+
+Example:
+make DESTDIR=/home/hedin/prj/cpupower uninstall
+
+
+running the tool
+----------------
+
+default directory
+-----------------
+
+$ sudo cpupower
+
+custom directory
+----------------
+
+When it comes to run the utility from the custom build catalog things
+become a little bit complicated as 'just run' approach doesn't work.
+Assuming that the current dir is '<your_custom_install_catalog>/usr',
+issuing the following command:
+
+$ sudo ./bin/cpupower
+will produce the following error output:
+./bin/cpupower: error while loading shared libraries: libcpupower.so.1:
+cannot open shared object file: No such file or directory
+
+The issue is that binary cannot find the 'libcpupower' library. So, we
+shall point to the lib dir:
+sudo LD_LIBRARY_PATH=lib64/ ./bin/cpupower
 
 
 THANKS