[PATCH 1 of 1] help: use 'digit' instead of 'byte' for width of ID in help/comment

[timeless]

it shouldn't be '-digit of', just ' digits'

> -    :``%H``: changeset hash (40 bytes of hexadecimal)
> +    :``%H``: changeset hash (40-digit of hexadecimal)

but that doesn't make it perfect-- just "less wrong".

i'm otherwise occupied for the next week or so. which means I can't
afford to think about this until later.