docs: point to the mailing lists and the tracker

docs: fix a typo in the configuration guide

Fixes: https://todo.hut.md/~reviewer/hello-hut/15

Add bash and zsh completions

Implements: https://todo.hut.md/~reviewer/hello-hut/9

docs: add a contributing guide

config: do not crash when $HOME is unset

Fixes: https://todo.hut.md/~reviewer/hello-hut/5

Add a logo

A small hut, drawn at 128x128.

docs: describe the configuration file

docs: add an installation guide