Document interpration of filenames and paths in config-file

This will prevent it being interpreted as if `.github/workflows/` were the working directory.

README.md

@@ -51,7 +51,7 @@ You customize the action by using the following variables:
 |:----------|:--------------|:-----------|
 |`use-quiet-mode`| Specify `yes` to only show errors in output.| `no`|
 |`use-verbose-mode`|Specify `yes` to show detailed HTTP status for checked links. |`no` |
-|`config-file`|Specify a [custom configuration file](https://github.com/tcort/markdown-link-check#config-file-format) for markdown-link-check. You can use it to remove false-positives by specifying replacement patterns and ignore patterns.|`mlc_config.json`|
+|`config-file`|Specify a [custom configuration file](https://github.com/tcort/markdown-link-check#config-file-format) for markdown-link-check. You can use it to remove false-positives by specifying replacement patterns and ignore patterns. The filename is interpreted relative to the repository root.|`mlc_config.json`|
 |`folder-path` |By default the `github-action-markdown-link-check` action checks for all markdown files in your repository. Use this option to limit checks to only specific folders. Use comma separated values for checking multiple folders. |`.` |
 |`max-depth` |Specify how many levels deep you want to check in the directory structure. The default value is `-1` which means check all levels.|`-1` |
 |`check-modified-files-only` |Use this variable to only check modified markdown files instead of checking all markdown files. The action uses `git` to find modified markdown files. Only use this variable when you run the action to check pull requests.|`no`|