External Issue: Disambiguate compile command in linear algebra documentation

16433, “CaptainSharf”, “Disambiguate compile command in linear algebra documentation”, “2020-09-22T16:39:10Z”

The compilation command in the documentation for linear algebra assumes the variables PATH_TO_LAPACKE_INCLUDE_DIR, PATH_TO_LIBGFORTRAN and PATH_TO_LAPACK_BINARIES to be set in the build environment. It would be a good idea to indicate that these variables need to be set before using the compile command given in the doc. We can optionally provide recommended values for these variables.