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
Proprietary platforms like Android and iOS are the competitors. These platforms are "walled", because of the stores, approval processes, closed decision making about the future of the platforms, and the owners.

Mentioning "walled" is kind of a cliche, I think.
http://readwrite.com/2011/08/10/knocking_down_apples_walled_garden_html5_vs_ios_apps