Add housing dataset XGB demo notebook
Add housing dataset XGB demo notebook

pair-code/what-if-tool,PAIR-code/what-if-tool,pair-code/what-if-tool,PAIR-code/what-if-tool,pair-code/what-if-tool,PAIR-code/what-if-tool,PAIR-code/what-if-tool,pair-code/what-if-tool,pair-code/what-if-tool,PAIR-code/what-if-tool