Add contribute section on README.md (#153)

It will help people join translation

Author: sotayamashita

README.md

@@ -14,3 +14,24 @@ npm install
 # serve
 npm run dev
 ```
+
+## Contribute
+
+[gl]: https://gitlocalize.com
+[gl-help]: https://docs.gitlocalize.com/ 
+[gl-issue-tracker]: https://github.com/gitlocalize/feedback
+[gl-repo]: https://gitlocalize/repo/101
+
+### Translation
+
+We are useing with a translation tool called [GitLocalize][gl] and follow the steps to get started with your contribution:
+
+1. Go to [GitLocalize's vuejs/vue-ssr-docs repository][gl-repo].
+1. Sign up using your GitHub account :octocat:.
+1. Find the document you are going to translate. 
+1. Happy translating :sparkles: .
+1. When you are done, send the translation for reviews.
+1. Reviewed translation will be sent as a Pull Request to GitHub by language admin in the community.
+
+To learn more about how GitLocalize works, visit their [help page][gl-help]. If you find any issues or feature requests, please file them in [GitLocalize's issue tracker][gl-issue-tracker].
+