chore(readme): add fixable

Author: azu

README.md

@@ -24,6 +24,12 @@ This rule check the spell by used with `prh.yml`.
 
 `rulePaths` : path to YAML file.
 
+### Fixable
+
+[![textlint rule](https://img.shields.io/badge/textlint-fixable-green.svg?style=social)](https://textlint.github.io/) 
+
+`textlint-rule-prh` support `--fix` feature of textlint.
+
 ### What is prh.yml?
 
 Please See [vvakame/prh](https://github.com/vvakame/prh "vvakame/prh").