Yes, it is actually a word. According to the 1913 Merriam Webster dictionary (via thefreedictionary.com), it is an adverbial variation of the adverb "soon" and simply means "soon." I suppose you would use it the same way?
For the poetic at heart or in mind, you now have another word to rhyme with -ly words. You should use it soonly. (Spell check does not agree that it is a word.)
