fix(license): add copyleft file

JulienChampagnol · JulienChampagnol · commit a0cfd3335e0b · 2023-09-20T14:19:36.000+02:00
diff --git a/COPYLEFT b/COPYLEFT
@@ -0,0 +1,4 @@
+## Dependencies
+
+VTK: BSD-3-Clause
+Copyright (c) 2008-Present Ken Martin, Will Schroeder, Bill Lorensen.
