qt_sink: add some warning on its usage

include/spdlog/sinks/qt_sinks.h

@@ -25,6 +25,8 @@ template<typename Mutex>
 class qt_sink : public base_sink<Mutex>
 {
 public:
+    // Warning: qt_sink won't be notified if the target QObject is destroyed.
+    // If the object's lifetime can be shorter than the logger's one, you should provide some permanent object and then use a standard signal/slot.
     qt_sink(QObject *qt_object, const std::string &meta_method)
     {
         qt_object_ = qt_object;
@@ -62,18 +64,24 @@ using qt_sink_st = qt_sink<spdlog::details::null_mutex>;
 //
 // Factory functions
 //
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(const std::string &logger_name, QTextEdit *qt_object, const std::string &meta_method = "append")
 {
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(const std::string &logger_name, QTextEdit *qt_object, const std::string &meta_method = "append")
 {
     return Factory::template create<sinks::qt_sink_st>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the object's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(
     const std::string &logger_name, QPlainTextEdit *qt_object, const std::string &meta_method = "appendPlainText")
@@ -81,6 +89,8 @@ inline std::shared_ptr<logger> qt_logger_mt(
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(
     const std::string &logger_name, QPlainTextEdit *qt_object, const std::string &meta_method = "appendPlainText")
@@ -88,12 +98,16 @@ inline std::shared_ptr<logger> qt_logger_st(
     return Factory::template create<sinks::qt_sink_st>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the objet's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(const std::string &logger_name, QObject *qt_object, const std::string &meta_method)
 {
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the objet's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(const std::string &logger_name, QObject *qt_object, const std::string &meta_method)
 {