Update Docker upgrade instructions

UPGRADING/v0_15.md

@@ -103,9 +103,30 @@ After the upgrade and migration complete, several follow-up steps are required o
     
     ```bash
     $ /opt/stalwart/bin/stalwart --config /opt/stalwart/etc/config.toml --console
+    Stalwart Server v0.15.2 Data Store CLI
+
     > delete y\x0c\x00 y\x12\xff
     > delete m\x0c\x00 m\x12\xff
+    > exit
     ```
+  - If you are using your database as the in-memory store with Docker:
+
+    ```bash
+    $ docker stop stalwart
+    $ docker run -it --rm \
+        -v <STALWART_DIR>:/opt/stalwart \
+        --entrypoint /usr/local/bin/stalwart \
+        stalwartlabs/stalwart:latest \
+        --config /opt/stalwart/etc/config.toml --console
+    Stalwart Server v0.15.2 Data Store CLI
+
+    > delete y\x0c\x00 y\x12\xff
+    > delete m\x0c\x00 m\x12\xff
+    > exit
+
+    $ docker start stalwart
+    ```
+
 
 ## Troubleshooting