When I recently searched for infos in this guide on how to create
a warning, I couldn't find any. Later I found it through #14.
The reason was that I didn't know the term 'diagnostics' and that
it is the collective term for errors, warnings and lints.
Renaming the chapter to include the word 'error' should help.
I think also including 'warning' in the title shouldn't be
neccessary, because it's close enought.
Julian Wollersberger