Add bug reporting clarification and examples to README

[HenryHansenK]

1. Updated README to include example of getting an artists image by using artist name.
2. Updated README to better show how and where bug reports should be reported.

[dieser-niko]

The README.md should be kept clean. Examples are given elsewhere. It should also be clear to everyone that the issue template should be filled in appropriately. And if people don't do that, then there's probably not going to be any change in their behaviour, even with an explanation in README.md.