Add documentation for user announcement/messaging (#6571)
Add documentation for user announcement/messaging (#6571)

Co-authored-by: Ino de Bruijn <f7dc43fb05ba7df7e769446605d0d8a8ab1011c4@ino.bio>

zhx828/cbioportal,mandawilson/cbioportal,sheridancbio/cbioportal,angelicaochoa/cbioportal,onursumer/cbioportal,angelicaochoa/cbioportal,angelicaochoa/cbioportal,zhx828/cbioportal,sheridancbio/cbioportal,angelicaochoa/cbioportal,onursumer/cbioportal,n1zea144/cbioportal,cBioPortal/cbioportal,onursumer/cbioportal,mandawilson/cbioportal,mandawilson/cbioportal,n1zea144/cbioportal,cBioPortal/cbioportal,zhx828/cbioportal,angelicaochoa/cbioportal,n1zea144/cbioportal,sheridancbio/cbioportal,n1zea144/cbioportal,mandawilson/cbioportal,onursumer/cbioportal,onursumer/cbioportal,cBioPortal/cbioportal,sheridancbio/cbioportal,cBioPortal/cbioportal,zhx828/cbioportal,sheridancbio/cbioportal,mandawilson/cbioportal,mandawilson/cbioportal,sheridancbio/cbioportal,cBioPortal/cbioportal,n1zea144/cbioportal,mandawilson/cbioportal,angelicaochoa/cbioportal,angelicaochoa/cbioportal,zhx828/cbioportal,n1zea144/cbioportal,zhx828/cbioportal,n1zea144/cbioportal,zhx828/cbioportal,cBioPortal/cbioportal,onursumer/cbioportal