DOCSP-29183 make sure gen.key is backup for upgrade (#5053) (#5059)

* DOCSP-29183 make sure gen.key is backup for upgrade

* Update source/includes/steps-upgrade-on-prem-from-archive.yaml



---------

Co-authored-by: zach-carr <[email protected]>

Author: kanchana-mongodb

source/includes/steps-upgrade-on-prem-from-archive.yaml

@@ -18,7 +18,7 @@ content: |
 
   On the |onprem| host that you're upgrading, back up your existing
   configuration files and logs to a directory other than the install
-  directory.
+  directory.    
 
   .. important::
 
@@ -34,6 +34,11 @@ content: |
 
         cp -a <install_dir>/conf ~/mms_conf.backup
         cp -a <install_dir>/logs ~/mms_logs.backup
+
+  You must also back up the ``gen.key`` file that |onprem| uses to
+  encrypt and decrypt |onprem|'s backing databases and user credentials. 
+  |onprem| requires an identical ``gen.key`` file on every
+  server that is part of a highly available |onprem| deployment. 
 ---
 stepnum: 3
 level: 4