`php tether help` ended with "Run 'tether help <command>'", and typing
exactly that gets "command not found" — tether is a file in the project
root, not a binary on the PATH. The Usage line of every command, the
hints printed by explain and make:feature, and the generate entries in
context all said the same. The docs have always written `php tether`.

The first thing a new user reads after the command list was an
instruction that does not work. It says `php tether` everywhere now, and
the two tests that pinned the old string pin the new one.