include obfs4 binary into the image

[ivanjx]

in alpine, the package that provides obfs4 is called lyrebird. after that is installed, users of this image can then add something like this into the torrc:

UseBridges 1
ClientTransportPlugin obfs4 exec /usr/bin/lyrebird
Bridge obfs4.......

reason:

1. to hide the fact that im using/connecting to the tor network at all from the ISP/government.
2. bypass censors that block regular tor connection.