Documentation of fromText should be updated for compatibility with text-2

[sjakobi]

text-short/src/Data/Text/Short/Internal.hs

Lines 698 to 704 in f037c38

	-- | \(\mathcal{O}(n)\) Construct 'ShortText' from 'T.Text'
	--
	-- This is currently not \(\mathcal{O}(1)\) because currently 'T.Text' uses UTF-16 as its internal representation.
	-- In the event that 'T.Text' will change its internal representation to UTF-8 this operation will become \(\mathcal{O}(1)\).
	--
	-- @since 0.1
	fromText :: T.Text -> ShortText

Note that O(1) is true only for the best case where the Text represents the full underlying ByteArray# rather than a slice of it.