build docs: list required Fedora packages

assigned to @vcunat

• We also have gnutls as required in our Makefile, and nettle as optional (for cookies);
• for docs, doxygen isn't enough and one needs sphinx+breathe;
• go isn't really used for anything but well...

When I think of it, knot-devel probably forces gnutls and nettle already :-)

mentioned in commit 3d82f1c3

merged

Should I send separate merge request to eradicate Go from the build system?

I don't feel strongly about that. For now I haven't taken any action to purge Go support from knot-resolver, as I could see little motivation to do so, even though we don't use it currently.