fix(nixfmt): update repo link and description (#505)
* feat(formatters): add nixfmt-rfc-style
docs: add nixfmt-rfc-style to readme and conform.txt
* feat: replace nixfmt with nixfmt-rfc-style
* doc: ensure description has period at the end
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Co-authored-by: Steven Arcangeli <506791+stevearc@users.noreply.github.com>
