- Only display the completions caveats from the current shell (assuming
it's one of Bash, ZSH or Fish)
- If the completions location isn't in the ZSH `FPATH` then link to the
documentation explaining how to do so.
Fixes https://github.com/Homebrew/brew/issues/8984
These instructions are currently incorrect and need to be ported to
`python` 3.x and `python@2` formulae. Until then it's better to not have
them than have them be incorrect.
Closes#3890.