add toolchange optimization notes

Author: ansonl

minimized-toolchanges-on-layer-change.md

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+# Toolchange Minimize Optimization Notes
+
+1. Look at all layer boundaries that are sandwiched between 2 other layer boundaries. Look at the layer boundaries that match this condition and have the fewest colors in the layer boundary first.
+
+    - Have the center layer boundary's layer change on the color that is least common (or not in) the 2 sandwiching layer boundaries