Akka.Cluster.Sharding migration docs: full restart of cluster (#6480)

* fixed 1.5 upgrade advisory

* clarified upgrade procedure

* fixed markdown linting errors

docs/community/whats-new/akkadotnet-v1.5-upgrade-advisories.md

@@ -59,14 +59,14 @@ akka.cluster.sharding{
 #### Migrating to New Sharding Storage From Akka.Persistence
 
 > [!NOTE]
-> This section applies only to users who were using `akka.cluster.sharding.state-store-mode = persistence` and `remember-entities=on`. If you were using `akka.cluster.sharding.state-store-mode = ddata` or not using `remember-entities` before then there is no migration of legacy data in your case.
+> This section applies to users who are using `remember-entities=on` and want to migrate to using the low-latency event-sourced based storage. All other users should just migrate to `state-store-mode=ddata`.
 
 Switching over to using `remember-entities-store = eventsourced` will cause an initial migration of data from the `ShardCoordinator`'s journal into separate event journals going forward.
 
 Upgrading to Akka.NET v1.5 will **cause an irreversible migration of Akka.Cluster.Sharding data** for users who were previously running `akka.cluster.state-store-mode=persistence`, so follow the steps below carefully:
 
 > [!IMPORTANT]
-> This migration is intended to be performed via upgrading Akka.NET to v1.5 and applying HOCON configuration changes - it requires no downtime.
+> This migration is intended to be performed via upgrading Akka.NET to v1.5 and applying the recommended configuration changes below - **it will require a full restart of your cluster any time you change the `state-store-mode` setting**.
 
 #### Upgrade to Akka.NET v1.5 Sharding
 
@@ -93,6 +93,13 @@ akka.cluster.sharding {
 }
 ```
 
+To deploy this upgrade:
+
+1. Take your cluster offline and
+2. Roll out the changes with the new version of Akka.NET installed and these HOCON changes.
+
+It should less than 10 seconds to fully migrate over to the new format and the Akka.Cluster.Sharding system will continue to start normally while it takes place.
+
 > [!NOTE]
 > If you don't run Akka.Cluster.Sharding with `remember-entities=on` normally then _there is no need to turn it on here_.
 
@@ -102,8 +109,6 @@ With these HOCON settings in-place the following will happen:
 2. Old `Akka.Cluster.Sharding.ShardCoordinator+IDomainEvent` will be upgraded to a new storage format via the `coordinator-migration` Akka.Persistence event adapter; and
 3. No more data will be persisted by the `ShardCoordinator` - instead it will all be replicated on the fly by DData, which is vastly preferable.
 
-It should take less than 120 seconds to fully migrate over to the new format and the Akka.Cluster.Sharding system will continue to operate normally while it takes place.
-
 > [!IMPORTANT]
 > This migration is irreversible once completed.