Create NEWS.md

[gavr123456789]

First of all, thank you for continuing to develop this wonderful library. The graph widget is exactly what I was missing in Vala + GTK when I came from the Qt world.

I suggest creating NEWS.md file that will contain the latest innovations, so that they are easier to navigate than by commits.

[lcallarec]

Hi @gavr123456789, thank you so much for your support, that means a lot to me.

Your suggestion is much appreciated, you're definitively right.

Here's the NEWS.md !