An update to the INSTALL file, in order to avoid a CMake error. In a detailed manner: the installation of the zlib1g-dev package avoided this CMake error:
CMake Error: The following variables are used in this project, but they are set to NOTFOUND. Please set them or make sure they are set and tested correctly in the CMake files: ZLIB_LIBRARY linked by target "kio_iso" in directory /home/user/krusader/iso
that affected some people (https://stackoverflow.com/a/49072832) for example when building Krusader under Ubuntu 18.04.