Addition of Meta Theme Colour Markup

Added suggested meta tag: For Colour Bleed/theme colour on Chrome UI on
Android (inline with current colour bleed trends, such as Yosemite/iOS8
etc).
Any CSS color is valid [as per the spec](https://github.com/whatwg/meta-theme-color). So it could be a 3-digit hex code, or just `blue`, or `rgb(0, 0, 0)`, etc.