HBASE-26439 improve upgrading doc (#3835)
HBASE-26439 improve upgrading doc (#3835)

Signed-off-by: Duo Zhang <ca823f7b4f21a31b6ef7892c1f90d53103f0d135@apache.org>
ndimiduk/hbase,ndimiduk/hbase,apurtell/hbase,Apache9/hbase,mahak/hbase,ndimiduk/hbase,apurtell/hbase,Apache9/hbase,apurtell/hbase,Apache9/hbase,ndimiduk/hbase,apurtell/hbase,apurtell/hbase,apurtell/hbase,apurtell/hbase,mahak/hbase,Apache9/hbase,Apache9/hbase,Apache9/hbase,mahak/hbase,mahak/hbase,Apache9/hbase,mahak/hbase,apurtell/hbase,apurtell/hbase,ndimiduk/hbase,mahak/hbase,ndimiduk/hbase,ndimiduk/hbase,ndimiduk/hbase,Apache9/hbase,mahak/hbase,mahak/hbase,ndimiduk/hbase,mahak/hbase,ndimiduk/hbase,Apache9/hbase,mahak/hbase,Apache9/hbase,apurtell/hbase