thermal: document __default_plot_settings()
diff --git a/cr2/thermal.py b/cr2/thermal.py
index 71c940f..9145c49 100644
--- a/cr2/thermal.py
+++ b/cr2/thermal.py
@@ -113,6 +113,11 @@
         plt.figure(figsize=(width, height))
 
     def __default_plot_settings(self, title=""):
+        """Set xlabel and title of the plot
+
+        This has to be called after the plot() command
+        """
+
         plt.xlabel("Time")
         if title:
             plt.title(title)