The /etc/shells file is not just documentation. It is used by various commands (e.g. chsh and probably its GUI equivalents) to decide if the shell you're trying to configure should be allowed or not.Long term, there may not be a 'first tier' shell in that /usr/local/bin/ location. The system-"approved" shells are in /etc/shells
Any time you install a new shell (on any UNIX-like system), you need to add it to /etc/shells. If you don't, then you probably won't be able to configure any accounts to actually use that shell without a lot of otherwise unnecessary hacking.