Creates an empty public-inbox or reinitializes an existing one.
It updates C<~/.public-inbox/config> by creating a
C<[publicinbox "NAME"]> section where
-C<publicinbox.NAME.mainrepo> is C<INBOX_DIR>,
+C<publicinbox.NAME.inboxdir> is C<INBOX_DIR>,
C<publicinbox.NAME.url> is C<HTTP_URL>, and
C<publicinbox.NAME.address> is C<ADDRESS>. Multiple addresses
may be specified for inboxes with multiple addresses.