update readme to reflect discord username change

[JamesKoenig]

Discord usernames have changed from the name#ident system to the current username system.

This change updates the contact information in the README associated with this tutorial.

I was debating changing the line to feature

• If you have trouble with the tutorial you can contact me on discord konijima (formerly Konijima#9279), or open an issue.

But that seemed to detract from the open an issue section.

Also I was debating putting the word 'at' or the phrase 'at username' before the current (actual) discord username konijima. That would read:

• If you have trouble with the tutorial you can contact me on discord at my username konijima or open an issue.

I can amend if any of these are preferred.