Show rustfmt action in example workflow

Show how the related rustfmt action can be used.

README.md

@@ -24,6 +24,19 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions-rust-lang/setup-rust-toolchain@v1
       - run: cargo test --all-features
+ 
+  # Check formatting with rustfmt
+  formatting:
+    name: cargo fmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      # Ensure rustfmt is installed and setup problem matcher
+      - uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          components: rustfmt
+      - name: Rustfmt Check
+        uses: actions-rust-lang/rustfmt@v1
 ```
 
 ## Inputs