CI - Check if README is up to date

Second attempt at checking if README is up to date in CI

.github/workflows/stable.yml

@@ -17,6 +17,23 @@ jobs:
         with:
           command: check
           args: --no-default-features
+
+  readme:
+    name: Readme
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - name: Install cargo-readme
+        run: cargo install cargo-readme
+      - name: Generate Readme for comparison
+        run: cargo readme > README_.md
+      - name: Check if readme is up to date
+        run: diff README.md README_.md
 
   test:
     name: Test Suite