Guidelines for translation contributors

Translators can go to POEditor to help translate shadowsocks-android.

Here's some guidelines:

• It's okay to leave some strings untranslated if you think it should use the same string as English (US).
• faq_url should not be changed. If you'd like to translate FAQ, submit a pull request with the translated faq.md (it should be named properly, e.g. .github/faq.zh-CN.md). Administrators will take care of the rest.