Add pages on graphics debugging and profiling

TODO:

- Document how to make use of markers in RenderDoc.
  Using `--verbose` doesn't seem to suffice for Vulkan on Linux at least
  (although it works on Windows in NSight).
- Document how to access shader sources in RenderDoc.
  Using `--generate-spirv-debug-info` currently doesn't work due to an engine bug.
- Document Radeon GPU profiling in graphics profiling page.
- Document Radeon Memory Visualizer in graphics profiling page.

Author: Calinou