Update README with check-update-db documentation

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

README.md

@@ -88,6 +88,34 @@ or success message when up to date.
 
 
 
+### wp core check-update-db
+
+Checks for the need for WordPress database updates.
+
+~~~
+wp core check-update-db [--network]
+~~~
+
+Compares the current database version with the version required by WordPress core
+to determine if database updates are needed.
+
+**OPTIONS**
+
+	[--network]
+		Check databases for all sites on a network.
+
+**EXAMPLES**
+
+    # Check if database update is needed
+    $ wp core check-update-db
+    Success: WordPress database is up to date.
+
+    # Check database update status for all sites on a network
+    $ wp core check-update-db --network
+    Success: WordPress databases are up to date on 5/5 sites.
+
+
+
 ### wp core download
 
 Downloads core WordPress files.