Logically re-apply64c70a8c4c("doc: point out that nixos-21.05 has gnuradio 3.9"), because it was lost in the conversion from docbook to markdown, in commit32c2dd304d("docs: nixos release notes to CommonMark (2105)"). (Apparently we have both .md and .xml release notes now, and CI fails unless they have the same content (after .md processing), so update the .xml file to match...)
Moved to: ./contributing-to-this-manual.xml. Link: https://nixos.org/manual/nixos/unstable/#chap-contributing