report filesystem space info of devices
$ make
# make install
$ make clean
# make uninstall
$ cmake -B build
$ cd build
$ make
# make install
$ cd build
# make uninstall
$ cd ..
$ rm -rf build
read the --help statement
when running "$ make" compiles the program and the binary is placed in the repo's main directory and build files in ./build
when running "# make install" the binary file is copied to /usr/bin/ldf , and the man page to /usr/share/man/man1/ldf.1
when running "$ make clean" the ./build is removed. And the binary is removed from the repo's directory but not from /usr/bin/ldf
when running "# make uninstall" the binary file is removed from /usr/bin/ldf as well as /usr/share/man/man1/ldf.1