add_new_files_to_doc.sh presumes bash is located in /usr/bin/bash

As title says, which is not portable (at least not for SL6).

https://unix.stackexchange.com/questions/206350/what-is-the-difference-if-i-start-bash-with-bin-bash-or-usr-bin-env-bash proposes instead:

#!/usr/bin/env bash