Add sqlite3 to dockerfile

docs/sql_cheatsheet.md

@@ -13,6 +13,15 @@ Feel free to use a visual Database editor like SqliteBrowser if you feel more co
 sudo apt-get install sqlite3
 ```
 
+### Using sqlite3 via docker-compose
+
+The freqtrade docker image does contain sqlite3, so you can edit the database without having to install anything on the host system.
+
+``` bash
+docker-compose exec freqtrade /bin/bash
+sqlite3 <databasefile>.sqlite
+```
+
 ## Open the DB
 
 ```bash