[libcalamares] Document JobQueue signals

src/libcalamares/JobQueue.h

@@ -60,8 +60,26 @@ public:
     bool isRunning() const { return !m_finished; }
 
 signals:
+    /** @brief Report progress of the whole queue, with a status message
+     *
+     * The @p percent is a value between 0.0 and 1.0 (100%) of the
+     * overall queue progress (not of the current job), while
+     * @p prettyName is the status message from the job -- often
+     * just the name of the job, but some jobs include more information.
+     */
     void progress( qreal percent, const QString& prettyName );
+    /** @brief Indicate that the queue is empty, after calling start()
+     *
+     * Emitted when the queue empties. The queue may also emit
+     * failed(), if something went wrong, but finished() is always
+     * the last one.
+     */
     void finished();
+    /** @brief A job in the queue failed.
+     *
+     * Contains the (already-translated) text from the job describing
+     * the failure.
+     */
     void failed( const QString& message, const QString& details );
 
 private: