See these last commits:
tulir/mautrix-signal@4fc34330c1f6947aece67863b0d04da34c776f80
tulir/mautrix-signal@64bc5c36a509ba435a0b01cf44afb1b5d2642efd
tulir/mautrix-signal@ddda1666d41d28750cc59d070e4388b24add6ad9
While it's kind of nice having it, it's also somewhat raw
and unnecessary.
Having a good default and not even mentioning it seems better
for most users.
People who need a more exposed bridge (rare) can use
override the default configuration using
`matrix_mautrix_signal_configuration_extension_yaml`.
teutat3s