Flamegraph chapter

[doyougnu]

Chapter for emitting and understanding flamegraphs in the context of GHC. Perhaps this moves to the GHC section because it relies on -prof?

some links:

• https://github.com/fpco/ghc-prof-flamegraph
• https://github.com/llelf/flamingra

[doyougnu]

also speedscope: https://mpickering.github.io/posts/2019-11-07-hs-speedscope.html