Add a 'reference' page

[tom]

For spectral parameterization, we have a doc page for "reference" (https://fooof-tools.github.io/fooof/reference.html).

This includes detailed information about what the reference paper to site, and also guides on what to report in a methods section, when using ByCycle. I think this kind of page is quite useful to promote good methods reporting.

In spectral-param there are also some related helper utilities built into the code to help get and report any used parameters. This might also make sense in bycycle too.