Update INSTALL.md

make install fails with 

    test -d "/usr/local/bin" || /usr/bin/install -c -d "/usr/local/bin"
    /usr/bin/install -c -d "/usr/local/lib/erlang"
    /usr/bin/install: cannot change permissions of ‘/usr/local/lib/erlang’: No such file or directory
    make: *** [install.dirs] Error 1
unless you run it as root. Changed HOWTO/INSTALL.md to reflect this.