(doc) update usbmuxd to libusbmuxd

[leonjza]

While both appear to still be the same version, a deprecation warning is shown when using homebrew to install usbmuxd. eg:

❯ brew info usbmuxd
Warning: Use libusbmuxd instead of deprecated usbmuxd
libusbmuxd: stable 2.0.2 (bottled), HEAD

❯ brew info libusbmuxd
libusbmuxd: stable 2.0.2 (bottled), HEAD