Change order of parameters and make explicit what is optional

Author: Guilherme Beltramini

README.md

@@ -11,19 +11,19 @@ Basic usage with all options enabled:
       - name: markdownlint-cli
         uses: nosborn/[email protected]
         with:
-          config_file: ".markdownlint.yaml"
           files: .
+          config_file: ".markdownlint.yaml"
           ignore_files: "examples/ignore/*"
           rules: "examples/rules/custom.js"
 
 ```
 
 ## Inputs
 
-* `config_file` - configuration file (JSON or YAML)
-* `files` - what to process, this is required - files, directories, globs
-* `ignore_files` - files to ignore/exclude - file, directory, glob
-* `rules` - custom rule files - file, directory, glob, package
+* `files` - what to process (files, directories, globs)
+* `config_file` (optional) - configuration file (JSON or YAML)
+* `ignore_files` (optional) - files to ignore/exclude (file, directory, glob)
+* `rules` (optional) - custom rule files (file, directory, glob, package)
 
 ## License