docs: "Introduce `allenvs` option for shell script execution"

- Add a new option `allenvs` in the README to pass all environment variables to the shell script.

Signed-off-by: appleboy <appleboy.tw@gmail.com>

README.md

@@ -47,6 +47,7 @@ See [action.yml](./action.yml) for more detailed information.
 | envs                    | Pass environment variables to shell script                      |               |
 | envs_format             | Flexible configuration of environment value transfer            |               |
 | debug                   | Enable debug mode                                               | false         |
+| allenvs                 | Pass all environment variables to shell script                  | false         |
 
 ## Usage