Added release notes for 3.26.0.9 (fixes a memory issue in multi-node XGBoost)
Added release notes for 3.26.0.9 (fixes a memory issue in multi-node XGBoost)

michalkurka/h2o-3,michalkurka/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,michalkurka/h2o-3,michalkurka/h2o-3,michalkurka/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,michalkurka/h2o-3,michalkurka/h2o-3