[v0.6.9] typo in help

[bo-ku-ra]

Subcommands:
(space x 2)d2.exe layout - Lists available layout engine options with short help
(space x 2)d2.exe layout [name] - Display long help for a particular layout engine, including its configuration options
(space x 2)d2.exe themes - Lists available themes
(space x 2)d2.exe fmt file.d2 ... - Format passed files
(\t)d2.exe play file.d2 - Opens the file in playground, an online web viewer (https://play.d2lang.com)