[QGIS-Developer] Processing doc - sphinx - anchors

[matteo]

> If I'm not wrong you already asked about it and Nyall had implemented this

yes that's right, but with was for groups and not single algorithm
names. With your fix of some hour ago the link of native algorithm looks
like:

https://docs.qgis.org/3.1/uk/docs/user_manual/processing_algs/qgis/interpolation.html#nativepackage

and not

https://docs.qgis.org/3.1/uk/docs/user_manual/processing_algs/qgis/interpolation.html#qgispackage

but that's alright. I'm changing the names manually. So I'll leave this
as it is and I think we really need to add a chapter to the
documentation guidelines for Processing (I'll do that).

Thanks

Matteo