Validate docs on CI

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

.github/workflows/ci.yml

@@ -25,6 +25,9 @@ jobs:
       - run: cargo fmt --all -- --check --files-with-diff
       - run: cargo clippy --all-targets -- -D warnings
       - run: cargo clippy --all-targets --all-features -- -D warnings
+      - run: cargo doc --no-deps
+        env:
+          RUSTDOCFLAGS: -Dwarnings
 
   tests:
     name: Tests