[boost] Release notes for release 1.69

To avoid forgetting to do it when release time comes, I would like to add some Math and Multiprecision library release notes for the next release 1.69 Is providing a PR for this file that way to do this? ( I speak Quickbook ;-) ) https://github.com/boostorg/website/blob/master/feed/history/boost_1_69_0.qb... (but it doesn't exist yet!) Thanks. Paul --- Paul A. Bristow Prizet Farmhouse Kendal UK LA8 8AB +44 (0) 1539 561830