year initialization

[coriolinus]

aoctool/README.md

Lines 33 to 39 in 2583817

	### TODO:
	If desired, initialize a top-level workspace in the current directory with
	```bash
	aoc year-init
	```

• set the year's configuration directory (see coriolinus/aoclib#8)
• ensure directory exists
• if no Cargo.toml, set up a Cargo workspace with a virtual manifest
• ensure /inputs/ in .gitignore