Document pre-existing data in fs mode (#5365)
Document pre-existing data in fs mode (#5365)

Document that pre-existing data in fs mode is safe and 
accessible

Fixes #5050
donatello/minio,vadmeste/minio,NitishT/minio,NitishT/minio,NitishT/minio,harshavardhana/minio,jimjag/minio,abperiasamy/minio,krishnasrinivas/minio,harshavardhana/minio,aead/minio,jimjag/minio,aead/minio,balamurugana/minio,minio/minio,rushenn/minio,harshavardhana/minio,abperiasamy/minio,harshavardhana/minio,aead/minio,harshavardhana/minio,balamurugana/minio,minio/minio,krishnasrinivas/minio,krishnasrinivas/minio,NitishT/minio,jimjag/minio,abperiasamy/minio,abperiasamy/minio,fwessels/minio,harshavardhana/minio,aead/minio,vadmeste/minio,rushenn/minio,krisis/minio,krisis/minio,fwessels/minio,rushenn/minio,donatello/minio,krishnasrinivas/minio,jimjag/minio,aead/minio,aead/minio,fwessels/minio,aead/minio,fwessels/minio,aead/minio,harshavardhana/minio,rushenn/minio,harshavardhana/minio