Documented the seam placement corner penalty with an image.

src/libslic3r/GCode/SeamPlacer.cpp

@@ -734,7 +734,7 @@ private:
         // ((ℯ^(((1)/(x^(2)*3+1)))-1)/(ℯ-1))*1+((1)/(2+ℯ^(-x)))
         // looks scary, but it is gaussian combined with sigmoid,
         // so that concave points have much smaller penalty over convex ones
-
+        // https://github.com/prusa3d/PrusaSlicer/tree/master/doc/seam_placement/corner_penalty_function.png
         return gauss(ccw_angle, 0.0f, 1.0f, 3.0f) +
                 1.0f / (2 + std::exp(-ccw_angle)); // sigmoid, which heavily favourizes concave angles
     }