docs: update the official docs

[neverchanje]

Because rdsn is originally a project from Microsoft, we didn't hardly modify the documentations since last year when we open sourced the internal fork of rdsn in xiaomi. Currently the xiaomi/rdsn has a large gap ahead of microsoft/rdsn, which is hardly maintained by its author (the latest commit is in Aug, 2017), therefore most of the documents are stale (like windows support).

We need to have the documentations caught up with the current actual state.