Add preliminary documentation for database conversion

docs/utils.md

@@ -554,6 +554,27 @@ Show whitelist when using a [dynamic pairlist](plugins.md#pairlists).
 freqtrade test-pairlist --config config.json --quote USDT BTC
 ```
 
+## Convert database
+
+`freqtrade convert-db` can be used to convert your database from one system to another (sqlite -> postgres, postgres -> other postgres), migrating all trades, orders and Pairlocks.
+
+Please refer to the [SQL cheatsheet](sql_cheatsheet.md#use-a-different-database-system) to learn about requirements for different database systems.
+
+```
+usage: freqtrade convert-db [-h] [--db-url PATH] [--db-url-from PATH]
+
+optional arguments:
+  -h, --help          show this help message and exit
+  --db-url PATH       Override trades database URL, this is useful in custom
+                      deployments (default: `sqlite:///tradesv3.sqlite` for
+                      Live Run mode, `sqlite:///tradesv3.dryrun.sqlite` for
+                      Dry Run).
+  --db-url-from PATH  Source db url to use when migrating database systems.
+```
+
+!!! Warning
+    Please ensure to only use this on an empty target database. Freqtrade will perform a regular migration, but may fail if entries already existed.
+
 ## Webserver mode
 
 !!! Warning "Experimental"