Add browser compatibility to README / Docs

[SirRawlins]

We should display browser compat for the status bar as part of the README/Docs as at the moment we don't really list any quirks.

Before we do this we need to do some extensive QA cross-browser to get a feeling for what does/doesn't work in the latest build, we can then look at fixing any issues.

To make testing easier I opened a gh-pages branch on the project so we can access the test setup and see the bar publicly whenever we want.

http://sorry-app.github.io/status-bar/

[SirRawlins]

@robingeall I think first steps in QA for new status bar is going to be to look at cross-browser testing, see if we come across any particular issues.

[SirRawlins]

Just registered for a free BrowserStack account to try and speed up the testing with various versions.

Seems the biggest issues at the moment are all with IE (no surprises there)

These stem from icons not loading properly on the latter versions, and the bar not working at all for versions 9 backwards.

[SirRawlins]

Here's a public link to the resulting screenshots.

https://www.browserstack.com/screenshots/2665e8b8bcefa96e278378e7cc098b84fb3ac3da

We'll open separate issues to deal with the individual problems.