docker: add single command docker build+run for btcd+lnd

This commit adds two Dockerfiles, along with a docker-compose file
which links the two docker files together allowing for single-command
deployment.

Using the docker-compose file, two containers are deployed. One running
btcd, and the other running lnd. Both containers share the same shared
volume mounted to the file system in order to allow land to read btcd’s
certificates for the TLS RPC connections.

Additionally, the btcd instance comes will an automatic RPC
configuration generated allowing one to use btcctl out of the box via
calls to “docker-compose exec btcctl …”.

docker/README.md

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