There are only two examples at the BBC (both poems, it seems), and the last one is from a poem in 1944, thus I am not quite sure how things are recently in terms of using this construction, but it seems to be rare, but understandable.
The meaning is, IMO, I need you to know/You should know, (I think) (that):
Apparently, the book A hand-book of present-day English (by E. Kruisinga) was written in 1914, so today -- nearly a hundred years later!-- there are bound to be a few things in that book that are no longer widely used. I've never heard anyone use "to" in the phrase "I'll have you know" when the meaning is basically "I'd like to point this out in order to be sure you know it". Howev