[doc] update readme.md

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

readme.md

@@ -19,7 +19,7 @@ It will provide you the below code structure:
 * gcdemu/: source code for the DPI library
 * configs/: default configurations for GCD and the testbench, which can be generated by elaborator
 * nix/: nix build script for the whole lowering process
-* build.sc & common.sc: Scala build script
+* build.mill & common.mill: Scala build script
 * flake.nix: the root for nix to search scripts
 
 ## Usage
@@ -145,7 +145,7 @@ To bump mill dependencies, run:
 nix build '.#gcd.gcd-compiled.millDeps' --rebuild
 ```
 
-and Then update `millDepsHash` in `nix/gcd/gcd.nix`
+and Then update `millDepsHash` in `nix/pkgs/dependencies/default.nix` and `nix/gcd/gcd.nix`
 
 ### Use the fetchMillDeps function
 
@@ -154,7 +154,7 @@ Fetch project dependencies for later offline usage.
 The `fetchMillDeps` function accept three args: `name`, `src`, `millDepsHash`:
 
 * name: name of the mill dependencies derivation, suggest using `<module>-mill-deps` as suffix.
-* src: path to a directory that contains at least `build.sc` file for mill to obtain dependencies.
+* src: path to a directory that contains at least `build.mill` file for mill to obtain dependencies.
 * millDepsHash: same functionality as the `sha256`, `hash` attr in stdenv.mkDerivation. To obtain new hash for new dependencies, replace the old hash with empty string, and let nix figure the new hash.
 
 This derivation will read `$JAVA_OPTS` environment varialble, to set http proxy, you can export:
@@ -171,15 +171,17 @@ Example:
 ```nix
 stdenv.mkDerivation rec {
     # ...
-    millDeps = fetchMillDeps {
-      inherit name;
-      src = with lib.fileset; toSource {
-        root = ./.;
-        fileset = unions [
-          ./build.sc
-        ];
+    passthru = {
+      millDeps = fetchMillDeps {
+        inherit name;
+        src = with lib.fileset;
+          toSource {
+            root = ./../..;
+            fileset = unions [ ./../../build.mill ./../../common.mill ];
+          };
+        buildInputs = with mill-dependencies; [ chisel.setupHook ];
+        millDepsHash = "sha256-NybS2AXRQtXkgHd5nH4Ltq3sxZr5aZ4VepiT79o1AWo=";
       };
-      millDepsHash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
     };
     # ...
     nativeBuildInputs = [
@@ -189,25 +191,6 @@ stdenv.mkDerivation rec {
 }
 ```
 
-### Use the `nvfetcherSource` attribute
-
-`projectDependencies` attribute is an nix setup hook that will obtain nvfetcher generated sources
-and place them under `dependencies` directory in build root.
-
-Read [nvfetcher](https://github.com/berberman/nvfetcher) document for nvfetcher usage.
-By default the `nvfetcherSource` attribute will read `nix/pkgs/dependencies/_sources/generated.nix`,
-so developer should place nvfetcher config and run `nix run .#nvfetcher` under `nix/pkgs/dependencies`.
-
-Usage:
-
-```nix
-stdenv.mkDerivation {
-    nativeBuildInputs = [
-        projectDependencies.setupHook
-    ]
-}
-```
-
 ## License
 
 The build system is released under the Apache-2.0 license, including all Nix and mill build system, All rights reserved by Jiuyang Liu <liu@Jiuyang.me>