Clarify solution wording for STAN-0208

> Possible solutions
> {Extra dependency} Switch to 'ByteString' from 'bytestring'

I get that `Text.length` is O(n), however applying the suggestion will yield incorrect results for characters wider than 1 byte (even assuming there's only UTF8). Basically, you can not get the length of the textual value by measuring it's memory footprint.

Start with issue #366 and the quoted “Possible solutions” wording for STAN-0208. Check the wording against the stated behavior of Text.length, ByteString, and bytestring; done means the suggestion accurately distinguishes textual character length from memory footprint.

Written by the indexing model from the issue text.