Update env.sample

Author: app-generator

Diff for: env.sample

@@ -8,3 +8,11 @@ JWT_SECRET_KEY=...    # edit value
 
 GITHUB_CLIENT_ID=...  # edit value
 GITHUB_SECRET_KEY=... # edit value 
+
+# If DB credentials (if NOT provided, or wrong values SQLite is used) 
+# DB_ENGINE=mysql
+# DB_HOST=localhost
+# DB_NAME=appseed_db
+# DB_USERNAME=appseed_db_usr
+# DB_PASS=pass
+# DB_PORT=3306