[JOSS REVIEW] Improve Install Instructions/ Process

[schuhmaj]

The issue

JOSS requires

Installation instructions: Is there a clearly-stated list of dependencies? Ideally these should be handled with an automated package management solution.

This bullet point is fulfilled, so this is not a blocking review criteria. However, I do have some suggestions to make EXP easier to set up.

Suggestions to improve installation instructions

• The installation's dependencies are not fully stated in the INSTALL.md. I mainly refer to the requirement to have the fftw or eigen3 library pre-installed
• The installation guide should ideally start with the requirements. As a new user, I am basically executing it step-by-step. However, the prerequisites (which are not automatically set-up via git submodules) eigen3, fftw are listed after the actual configuration with CMake. I would recommend to re-order this.

Suggestions to improve CMake Build System overall

Alternatively, I would recommend embracing the existing CMake build system more:

• You can set up the FFTW or HDF5 (and the other) libraries via CMake's Fetch Content Module. Both libraries offer tar balls containing a CMakeList.txt. E.g.

FetchContent_Declare(
  fftw
  URL      http://fftw.org/fftw-3.3.10.tar.gz
  URL_HASH MD5=8ccbf6a5ea78a16dbc3e1306e234cc5c
)

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This issue is part of the JOSS review: openjournals/joss-reviews#7302