add japanese translate

Hi all.

I wanna advocate this manifesto and principle of Extensible Web to Japanese web devs.

I think this thought is quite important for web future, so I wanna join this as possible as I can.
in japan, there are lots of powerful web developer, but it seem for me that they don't no about this manifesto well.
at first, I translate this in Japanese. but I don't know how publish it.

so I create this PR for asking you.

if it's works fine for you, I'm appreciate it if you publish this for example at https://ja.extensiblewebmanifesto.org/ 
or if that dosen't works. please let me to publish this at my own domain (https://jxck.io) or on my blog (http://jxck.hatenablog.com).

also, thanks for your every works for web.

thanks, and sorry for my poor english ;p

Jxck
"オープンな Web が取り囲む競合と競うためには、 Web 開発者の良いアイデアを、Web のインフラの一部とするための、はっきりとした手段が必要です。" seems fine.

"its walled competitors" seems "competitors who build walls around the open web" isn't it?
this said that web need the power as a platform to compete with other platform.

who is "competitors who build walls around developers" ? 
standarization ?