Update Qt and QML coding guidelines

guidelines/Qt-and-QML-coding-guidelines.md

-# Qt
+# Qt/c++
 ## Signal and slot naming
 Both signals and slots should use camelCase.
 A signal should use the simple past tense or past participle of some verb, likely prefixed by a short subject. A corresponding slot should be the signal prefixed with the word "on" and not the word "slot". Here are some examples: