Improved README - Usage for supported and unsupported devices

[ballerburg9005]

Please accept this PR or improve your README in a similar way.

Like outlined, there are only a handful of reset strategies for most unsupported cards according to the amdgpu driver, and thus chances are quite high that you can make it work simply via trial and error with one of the already implemented methods in vendor-reset (even if those do not encompass all strategies that the amdgpu driver employs, insofar as this is even so - and even if the strategies are misfit, it can still work somehow and be better than nothing - and even if whatever important, diverse and manifold use cases people have for doing this, are not immediately or ever at all apparent).

However it is VERY difficult and counter-intuitive to understand this for people from the outside, without some major research and knowledge about hardware. And the whole project is quite suggestive that it is not feasible for a mere end user to make unsupported cards work (which is maybe in the realm of half-truths at best). So it would be prudent and pertinent to briefly explain the situation like this in a practical manner upfront in the README, in order to not send everyone (i.e. mostly less-qualified people) on the roller coaster that entails finding tricks to make unsupported hardware work somehow, or to bail out of trying, despite their cards actually working with very fair chance.