Support setting nix_path (#2)

README.md

@@ -21,11 +21,27 @@ This GitHub Action sets nix for use in CI.
       cachix_auth_token: '${{ secrets.CACHIX_AUTH_TOKEN }}'
 ```
 
+By default, this action assumes that:
+* You are using the `niteo` cachix cache.
+* You have `./nix/default.nix` in your repo where nix can find nixpkgs.
+
+You can set your project specific values like so:
+
+```yaml
+  - name: Configure nix
+    uses: teamniteo/gha-actions/nix@main
+    with:
+      cachix_auth_token: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      cache: myproject
+      nix_path: nixpkgs=nixos-unstable
+```
+
+
 # Uncommited changes Action
 
 This GitHub Action checks if there are uncommited or not ignored files present after the steps ran.
 
 ```yaml
   - name: Check for uncommitted-changes
     uses: teamniteo/gha-actions/uncommitted-changes@main
-```
+```

nix/action.yml

@@ -4,18 +4,20 @@ description:
   derivations to cache
 
 inputs:
-  cache:
-    default: niteo
   auth_token:
     required: true
+  cache:
+    default: niteo
+  nix_path:
+    default: nixpkgs=./nix/default.nix
 
-
 runs:
   using: "composite"
   steps:
     - uses: cachix/install-nix-action@v22
       with:
-        nix_path: nixpkgs=channel:nixos-unstable
+        nix_path: ${{ inputs.nix_path }}
+
     - uses: cachix/cachix-action@v12
       with:
         name: ${{ inputs.cache }}