add copy/paste and erase selecton buttons

README.md

@@ -4,12 +4,12 @@
 logic mostly like https://git.crispypin.cc/CrispyPin/marble
 
 ## todo
-- copy/cut/paste selections
 - undo/redo
 - more levels
 - make marble movement symmetric and order-independent
 - make power propagation not recursive
 - story/lore
+- cut selections, copy to system clipboard
 - timestamps in solutions and blueprints
 - multiple input/output sets
 - tooltips