This patch does 2 things:

1. also looks for explanations of manuallevel checkers
2. provides a nice message if the user mistyped the checker name

$ clazy --explain tr-non-ladsfa
There is no explanation available for checker "tr-non-ladsfa"
Run 'clazy --explain' to see the list of all available checkers.

$ clazy --explain tr-non-

Explanation for checker tr-non-literal (manuallevel)

tr-non-literal

Finds calls to QObject::tr() with non literal argument.

Example: tr(myStr.toUtf8());