add cargo doc to workflow

Author: hellow554

.github/workflows/main.yml

@@ -32,7 +32,7 @@ jobs:
             rust: stable-x86_64-gnu
     steps:
     - uses: actions/checkout@master
-    - name: Install Rust (rustup)
+    - name: Install Rust
       run: |
         rustup update ${{ matrix.rust }} --no-self-update
         rustup default ${{ matrix.rust }}
@@ -60,6 +60,19 @@ jobs:
         rustup component add rustfmt
     - run: cargo fmt -- --check
 
+  doc:
+    name: Check Documentation
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Install Rust
+      run: |
+        rustup update stable --no-self-update
+        rustup default stable
+        rustup component add rust-docs
+    - name: Run rustdoc
+      run: RUSTDOCFLAGS="-D warnings" cargo doc --verbose
+
   features:
     name: Feature check
     runs-on: ubuntu-latest