build: add pandoc to nix derivation

flake.nix

@@ -33,6 +33,7 @@
           buildInputs = [
             rust
             pkgs.libnotify
+            pkgs.pandoc
           ];
 
           shellHook = ''
@@ -54,7 +55,15 @@
             patchelf $out/bin/hinoirisetr --add-rpath ${pkgs.libnotify}/lib
           '';
 
-          nativeBuildInputs = [ ];
+          postBuild = ''
+            pandoc manpages/hinoirisetr.1.md -s -t man -o $out/share/man/man1/hinoirisetr.1
+          '';
+
+          preBuild = ''
+            mkdir -p $out/share/man/man1
+          '';
+
+          nativeBuildInputs = [ pkgs.pandoc ];
           buildInputs = [ pkgs.libnotify ];
         };
       }