prevent unauthorized access to administrative db0 when connection to redis-cli

docs/admin.md

@@ -80,6 +80,7 @@ Keys in `DB 0` (internal layout, but useful to understand how things work):
   - Requires the exact admin secret as the `KEY` argument to `SELECT 0`
   - Permission is `ReadWrite` when the secret matches
 
+Connections start with no database selected. Any command that requires storage (GET, SET, H*, L*, SCAN, etc.) will return an error until you issue a SELECT to choose a database. Admin DB 0 is never accessible without authenticating via SELECT 0 KEY <admin_secret>.
 ### How to select databases with optional `KEY`
 
 - Public DB (no key required)