Add exercises.

exercises/parallelism.qmd

+---
+title: "Parallelism"
+---
+### Tasks:
+  1. Revisit `schedule` and try `schedule(dynamic,100)` as in the hands-on and
+     explain what happens and why that differs from `schedule(static, 100)`.
+  42. Parallelize the loop in `maxval`. Search for the comment
+     `// HOMEWORK: Parallelise this loop!`. All information needed can be found
+     in the lecture slides.
+  23.  Do a strong-scaling experiment starting with 2 threads and up to 32
+      threads and plot the result.
+  42. If you were to increase the number of threads, do you expect the speedup
+      to continue indefinitely? If not, which limits can you imagine? Feel free
+      to use kitchen metaphors.