Add docs for MIMIR_AUTH_TOKEN

operations/mimir-rules-action/README.md

@@ -11,6 +11,7 @@ This action is configured using environment variables defined in the workflow. T
 | `MIMIR_ADDRESS`              | URL address for the target Mimir cluster                                                                                                                                                                                                                                                           | `false`  | N/A     |
 | `MIMIR_TENANT_ID`            | ID for the desired tenant in the target Mimir cluster. Used as the username under HTTP Basic authentication.                                                                                                                                                                                       | `false`  | N/A     |
 | `MIMIR_API_KEY`              | Optional password that is required for password-protected Mimir clusters. An encrypted [github secret](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/creating-and-using-encrypted-secrets) is recommended. Used as the password under HTTP Basic authentication. | `false`  | N/A     |
+| `MIMIR_AUTH_TOKEN`           | Optional bearer or JWT token that is required for Mimir clusters authenticating by bearer or JWT token. An encrypted [github secret](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/creating-and-using-encrypted-secrets) is recommended.                         | `false`  | N/A     |
 | `ACTION`                     | Which action to take. One of `lint`, `prepare`, `check`, `diff` or `sync`                                                                                                                                                                                                                          | `true`   | N/A     |
 | `RULES_DIR`                  | Comma-separated list of directories to walk in order to source rules files                                                                                                                                                                                                                         | `false`  | `./`    |
 | `LABEL_EXCLUDED_RULE_GROUPS` | Comma separated list of rule group names to exclude when including the configured label to aggregations. This option is supported only by the `prepare` action.                                                                                                                                    | `false`  | N/A     |