message: Add general comments on header additions.
diff: @@ -396,6 +396,11 @@ General rules:
  _Note_: Please see the detail in the `dev_tools/scripts/config`.
  +#### Some general comments.
  +
  +1. Private headers of Ginkgo should not be included within the public Ginkgo header.
  +2. It is a good idea to keep the headers self-sufficient, See [Google Style guide for reasoning](https://google.github.io/styleguide/cppguide.html#Self_contained_Headers).
  +3. The recommendations of the `iwyu` (Include what you use) tool can be used to make sure that the headers are self-sufficient and that the compiled files ( `.cu`, '.cpp', `.hip.cpp` ) include only what they use. A [CI pipeline](https://gitlab.com/ginkgo-project/ginkgo-public-ci/-/jobs/584358356) is available that runs with the `iwyu` tool. Please be aware that this tool can be incorrect in some cases.
  #### Automatic header arrangement
  