Add anchor links to section headers

[jonek]

The sections headers already have ids that can be used as anchors.

It would be very convenient to show an anchor symbol next to the section header on hover.
That would it make easier to copy deep links into the documentation.

An example can be found in the Cordova documentation.
See: https://cordova.apache.org/docs/en/latest/guide/hybrid/plugins/index.html