T7253: Improve documentation about upgrades with recommendations

Improve the documentation about upgrades and rollbacks with information about how to handle settings.

content/designs/system-updates-and-rollback.md

@@ -757,7 +757,7 @@ As explained, during an upgrade, a new commit is applied on the `OSTree` repo,
 which modifies the read-only partitions, but does not modify the read-write
 ones. To handle the upgrade of system settings stored in `/etc` a copy of its
 default values is kept in `/usr/etc` which is updated with the new commit.
-hanks to this information `OSTree` can detect the files that have been changed
+Thanks to this information `OSTree` can detect the files that have been changed
 and apply a 3-way merge, to update the `/etc`.
 
 This process allows to update settings to new defaults for files that were not