new readme about the sandbox
new readme about the sandbox

miguel0afd/crossdata,gserranojc/Crossdata,Stratio/crossdata,jjlopezm/crossdata,compae/Crossdata,ccaballe/crossdata,compae/Crossdata,hdominguez1989/Crossdata,pmadrigal/Crossdata,luismcl/crossdata,ccaballe/crossdata,jjlopezm/crossdata,darroyocazorla/crossdata,miguel0afd/crossdata,darroyocazorla/crossdata,hdominguez1989/Crossdata,pfcoperez/crossdata,Stratio/crossdata,luismcl/crossdata,gserranojc/Crossdata,pmadrigal/Crossdata,pfcoperez/crossdata