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
How about "ブラウザベンダ由来のライブラリ", because "ブラウザ由来のライブラリ" sounds like "implemented as browsers' functionality, and extracted as libraries later" which is opposite to the recommended approach.

It can be translated as "browser vendor-initiated libraries", not "browser-initiated libraries", but Polymer was initiated by Google, not Chrome, X-Tags was initiated by Mozilla, not Firefox.