Minor password manager documentation bug

[Alexander Clouter]

Just a documentation bug on how to use a password manager.

Clearly expected back is just the password from running pass but the majority of users will have multiline files so a multiline value would be returned causing some brief confusion.

As a suggestion, you might want to be more explicit with something like:

password_cmd = "/bin/bash -o pipefail -c 'pass spotify.com/username | head -n1'"