Add git bisect reference as general strategy

lectures/debugging-strategies/slides.qmd

@@ -36,7 +36,8 @@ digraph {
  - Narrow down the code where the error occured (divide and conquer)
  - Use a debugger
  - Did it work before? What changed since?
-
+ - If changes are committed in a repo,
+   find the last valid commit (`git bisect`)
 
 
 # Compile-time errors {.leftalign}