[DOCs][Fixed] Typo in panelization output

From #517

kibot/out_panelize.py

@@ -463,7 +463,7 @@ class PanelizeSource(PanelOptions):
     def __init__(self):
         with document:
             self.type = 'auto'
-            """ *[auto,rectangle,annotation] How we select the area of the PCB tu used for the panelization.
+            """ *[auto,rectangle,annotation] How we select the area of the PCB used for the panelization.
                 *auto* uses all the area reported by KiCad, *rectangle* a specified rectangle and
                 *annotation* selects a contour marked by a kikit:Board footprint """
             self.stack = 'inherit'