Add further performance notes from vtune and 2D heat diffusion.

4 jobs from master in 3 minutes 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #3075
build_cmake

00:44

 
  Test
passed #3076
run_tests

00:44

 
  Sanitizer
passed #3078
run_address_sanitizer

01:24

passed #3077
run_thread_sanitizer

00:57