docs(readme): add note about updating completions

Author: va-an

README.md

@@ -236,6 +236,8 @@ This is available for wallet, key, repl and compile features. When ommitted, out
 bdk-cli completions --help
 ```
 
+Completion files are generated from the currently installed binary. After upgrading `bdk-cli`, re-run the `completions` command to keep them in sync with the new version.
+
 ## Saving and using wallet configurations
 
 The `wallet config` sub-command allows you to save wallet settings to a `config.toml` file in the default directory (`~/.bdk-bitcoin/`) or custom directory specified with the `--datadir` flag. This eliminate the need to repeatedly specify descriptors, client types, and other parameters for each command. Once configured, you can use any wallet command by simply specifying the wallet name. All other parameters are automatically loaded from the saved configuration.