Provide alternative to rcon and attach for sending commands

[itzg]

From discussion https://discord.com/channels/660567679458869252/660569755320844308/895439654017445898

[itzg]

Uses --named-pipe added to https://github.com/itzg/mc-server-runner/releases/tag/1.8.0

[itzg]

Added description of mc-send-to-console in middle of

https://github.com/itzg/docker-minecraft-server#interacting-with-the-server