docs: add language support

• Add language support example for cjk language
• Add an image to show how to enable IME in the browser

Related issues: #12 #22 #60 #91

@sytone This commit explained how to display CJK correctly without download any TTF files and also let everyone know how to use their own IME to input other language. And can also close the issue #60 #91.

Validated on RIME (An open source Chinese IME), I think the IME option should works to every IME.

Thanks!