add docs build to CI

Author: mplanchard

.github/workflows/ci.yml

@@ -99,10 +99,28 @@ jobs:
           command: "fmt"
           args: "--all -- --check"
 
+  docs:
+    name: "Docs"
+    runs-on: "ubuntu-latest"
+    env:
+        RUSTDOCFLAGS: "-D warnings"
+    steps:
+      - uses: "actions/checkout@v2"
+      - uses: "actions-rs/toolchain@v1"
+        with:
+          profile: "minimal"
+          toolchain: "stable"
+          override: true
+      - uses: "actions-rs/cargo@v1"
+        with:
+          command: "doc"
+          args: "--no-deps"
+
   Verify:
     name: "Verify"
     runs-on: "ubuntu-latest"
     needs:
+      - "docs"
       - "fmt"
       - "test"
       - "lint"