Add --from-auto-update to known flags

The updater invokes the updated program with --from-auto-update
this caused the app to not start since we switched to QCommandLineParser
since it aborts on unknown flags. We should probably use QCommandLineParser::parse
instead of ::process since that doesn't abort on failure but for now
this was a simpler change.

src/main.cpp

@@ -88,6 +88,7 @@ int main(int argc, char *argv[])
     parser.addHelpOption();
     parser.addVersionOption();
     parser.addOptions({{{"l", "licenses"}, "Show license information"}});
+    parser.addOptions({{{"a", "from-auto-update"}, "When invoked from auto-update"}});
 
     char **newArgv = appendCommandLineArguments(argc, argv, g_qtFlags);
     argc += g_qtFlags.size();