#15158 (review) mentioned several ways that the documentation for spack external find could be substantially improved:

• Provide a code example of implementing determine_spec_details for a package
• Explain how to define executables to look for (and also e.g. that they are treated as regular expressions and so can pull in unexpected files).
• Add the "why" for a couple of constraints (i.e. explain that this logic only works for build/run deps because it examines PATH for executables)