Inline the submodule of themes/hermit with a git-subtree

Add 'themes/hermit/' from commit '56843f347a642324970ba30d58f23c64e037bb7c'

git-subtree-dir: themes/hermit
git-subtree-mainline: 7844fa5501c271b1b2b5ece2cb19f3202cd6e5ad
git-subtree-split: 56843f347a

flake.nix

@@ -3,12 +3,7 @@
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
 
-  inputs.hermit = {
-    url = "github:vojta001/hermit/tmp";
-    flake = false;
-  };
-
-  outputs = { self, nixpkgs, hermit }:
+  outputs = { self, nixpkgs, }:
   let
     pkgs = import nixpkgs { system = "x86_64-linux"; };
   in
@@ -18,12 +13,6 @@
         pname = "vkane.cz";
         version = "";
         src = self;
-        # the theme is included as a submodule, and with nix it is an alchemy whether it is somehow included or not (in which case the empty parent directory might be missing)
-        preConfigure = ''
-          rm --dir --force themes/hermit
-          mkdir -p themes
-          ln --symbolic '${hermit}' themes/hermit
-        '';
         buildPhase = ''
           '${pkgs.hugo}'/bin/hugo --buildExpired --buildFuture --destination "$out" --minify --printPathWarnings --printI18nWarnings
         '';