doc(README): link to GH Pages, describe references

This commit edits the root directory's README.md file to
1. Add a link to the FORD documentation on GitHub Pages and
2. Add descriptions of the possible utility of the documentation
   of other netlib/fftpack-based libraries.

Author: rouson

README.md

@@ -64,7 +64,18 @@ meson configure build --prefix=/path/to/install
 meson install -C build
 ```
 
-## Links
-- [netlib/dfftpack1.0(fftpack4.0)](http://www.netlib.org/fftpack/)
-- [Documents of fft routines in GNU/gsl based on `netlib/fftpack`](https://www.gnu.org/software/gsl/doc/html/fft.html#)
-- [Documents of scipy.fftpack](https://docs.scipy.org/doc/scipy/reference/fftpack.html)
+## Documentation
+See [https://fortran-lang.github.io/fftpack/](https://fortran-lang.github.io/fftpack/) for documentation generated by this repository's [FORD] [project file].
+
+## References 
+- [Recommended reference]: Although this SciPy version is in Python and the procedures have different arguments from [fortran-lang/fftpack], the SciPy fftpack documentation provides a succinct description of the storage sequence for the function results in both scipy.fftpack and [fortran-lang/fftpack], e.g., the storage sequence for the `rfft` function result.
+- [Historical reference]: This is the netlib/fftpack library on which [fortran-lang/fftpack] is based but the two are _not_ interface-compatible.
+- [Theory reference]: The documentation for the GNU/gsl FFT routines, which is also based on netlib/fftpack, provides some useful definitions of FFT terminology and represenations of the analytical forms of the Discrete Fourier Transform nicely formatted by [LaTeX].
+
+[FORD]: https://github.com/Fortran-FOSS-Programmers/ford
+[project file]: ./API-doc-FORD-file.md
+[fortran-lang/fftpack]: https://github.com/fortran-lang/fftpack
+[Recommended reference]: https://docs.scipy.org/doc/scipy/reference/fftpack.html
+[Historical reference]: http://www.netlib.org/fftpack/
+[Theory reference]: https://www.gnu.org/software/gsl/doc/html/fft.html#
+[LaTeX]: https://www.latex-project.org