Update setting of the environment variables

[polyluxus]

In recent versions, with the script there was always the error message that XTBHOME was unset. This is annoying even though it works. Setup should reflect the following: https://xtb-docs.readthedocs.io/en/latest/setup.html

#!/usr/bin/env bash
# requirements: $XTBHOME is set to `xtb` root directory
# otherwise the script will find the location of itself here:
if [ -z "${XTBHOME}" ]; then
   XTBHOME="$(cd -P "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
fi

# set up path for xtb, using the xtb directory and the users home directory
XTBPATH=${XTBHOME}/share/xtb:${XTBHOME}:${HOME}

# to include the documentation we include our man pages in the users manpath
MANPATH=${MANPATH}:${XTBHOME}/share/man

# finally we have to make the binaries and scripts accessable
PATH=${PATH}:${XTBHOME}/bin
LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:${XTBHOME}/lib
PYTHONPATH=${PYTHONPATH}:${XTBHOME}/python

export PATH XTBPATH MANPATH LD_LIBRARY_PATH PYTHONPATH

Apparently also the location of the man files was changed, which may lead to a problem...

Should be finished with the real release of xtb 6.3.0.