Enable easily citing RFCs

Nix (with flakes) has an annoying behaviour where a Git subproject won't automatically be available, so a workaround is required.
See NixOS/nix#5284 and NixOS/nix#12421.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "report/rfc.bib"]
+	path = report/rfc.bib
+	url = https://github.com/ichdasich/rfc.bib.git

flake.nix

@@ -9,6 +9,11 @@
 
     disko.url = "github:nix-community/disko";
     disko.inputs.nixpkgs.follows = "nixpkgs";
+
+    rfc-bib = {
+      url = "git+file:report/rfc.bib";
+      flake = false;
+    };
   };
 
   outputs = { self, ... }@inputs: let
@@ -84,6 +89,7 @@
       inherit measurements;
       report = import ./report/build-document.nix {
         inherit lib pkgs;
+        inherit (inputs) rfc-bib;
         texlive = get-latex-packages pkgs;
         shellEscape = true;
         minted = true;

report/build-document.nix

@@ -6,6 +6,7 @@
 
 { lib
 , pkgs
+, rfc-bib
 
 # Name of the final pdf file
 , name ? "document.pdf"
@@ -52,17 +53,28 @@ let
     extraFlags
     (lib.optional shellEscape "-shell-escape")
   ];
+  report-src = fs.toSource {
+    root = ./.;
+    fileset = fs.unions [
+      ./.latexmkrc
+      (fs.fileFilter (file: file.hasExt "tex" || file.hasExt "eps" || file.hasExt "sty" || file.hasExt "bib" || file.hasExt "dbx") ./.)
+    ];
+  };
+  rfc-bib-src = pkgs.linkFarm "rfc.bib-src" [{
+    name = "rfc.bib";
+    path = rfc-bib;
+  }];
 in
 
 assert minted -> shellEscape;
 
 pkgs.stdenvNoCC.mkDerivation rec {
   inherit name;
-  src = fs.toSource {
-    root = ./.;
-    fileset = fs.unions [
-      ./.latexmkrc
-      (fs.fileFilter (file: file.hasExt "tex" || file.hasExt "eps" || file.hasExt "sty" || file.hasExt "bib" || file.hasExt "dbx") ./.)
+  src = pkgs.symlinkJoin {
+    name = "combined-report-src";
+    paths = [
+      report-src
+      rfc-bib-src
     ];
   };
 

report/header.tex

@@ -50,6 +50,7 @@
 \input{Environments.tex}
 
 \addbibresource{bibliography.bib}
+\addbibresource{rfc.bib/rfc.bib}
 
 %% Geometrie
 \newdimen\lines