update documentation about 0.db admin db + symmetric encryption + include RPC examples + asymmetric transpart named key instances for encryption and signatures

docs/cmds.md

@@ -122,4 +122,27 @@ redis-cli -p 6379 --rdb dump.rdb
 
 # Import to sled
 redis-cli -p 6381 --pipe < dump.rdb
+```
+
+## Authentication and Database Selection
+
+HeroDB uses an `Admin DB 0` to govern database existence, access and per-db encryption. Access control is enforced via `Admin DB 0` metadata. See the full model in `docs/admin.md`.
+
+Examples:
+```bash
+# Public database (no key required)
+redis-cli -p $PORT SELECT 1
+# → OK
+```
+
+```bash
+# Private database (requires access key)
+redis-cli -p $PORT SELECT 2 KEY my-db2-access-key
+# → OK
+```
+
+```bash
+# Admin DB 0 (requires admin secret)
+redis-cli -p $PORT SELECT 0 KEY my-admin-secret
+# → OK
 ```