Docs images from Imgur no longer work in the UK

[dannytaurus]

Since Imgur recently stopped service in the UK, the images in the docs that are hosted there no longer work.

Docs issue here: https://github.com/christophhart/hise_documentation/issues/56

Happy to contribute if someone can tell me where to put the images instead.

EDIT: example here (if you're in the UK): https://docs.hise.dev/scriptnode/101/gain_example.html