Add a "signals and callbacks" chapter into the first steps document

doc/first-steps.md

@@ -591,7 +591,6 @@ int main (int argc, char* argv[])
   return app.exec();
 }
 ```
-```
 *(Note: You can close the window with the mouse, 
 <kbd>Shift</kbd>+<kbd>F10</kbd> or <kbd>Ctrl</kbd>+<kbd>^</kbd>)*
 

src/ffiledialog.cpp

@@ -803,7 +803,7 @@ void FFileDialog::cb_processRowChanged (FWidget*, FDataPtr)
   if ( n == 0 )
     return;
 
-  const auto& name = dir_entries[n - 1].name;
+  const auto& name = FString(dir_entries[n - 1].name);
 
   if ( dir_entries[n - 1].directory )
     filename.setText( name + '/' );