Add instructions for MongoDB to README_DATABASE
Add instructions for MongoDB to README_DATABASE

lamptt/ChicagoBoss,ChicagoBoss/ChicagoBoss,yunkai/ChicagoBoss,synlay/ChicagoBoss,lamptt/ChicagoBoss,frkarl/ChicagoBoss,aherranz/ChicagoBoss,yunkai/ChicagoBoss,synlay/ChicagoBoss,powermedia/ChicagoBoss,solatis/ChicagoBoss,danikp/ChicagoBoss,solatis/ChicagoBoss,uselessd/ChicagoBoss,7i11/ChicagoBoss,ChicagoBoss/ChicagoBoss,uselessd/ChicagoBoss,powermedia/ChicagoBoss,danikp/ChicagoBoss,frkarl/ChicagoBoss,7i11/ChicagoBoss,aherranz/ChicagoBoss