Add GitHub action that runs clippy on every push

This is copy-pasted from https://github.com/marketplace/actions/rust-clippy-check

Test Plan: submit this commit as pull request, check this action is executed

Reviewers: jozef-mokry

Reviewed By: jozef-mokry

Pull Request: #37

.github/workflows/clippy.yml

@@ -0,0 +1,12 @@
+on: push
+name: Clippy check
+jobs:
+  clippy_check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - run: rustup component add clippy
+      - uses: actions-rs/clippy-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          args: --all-features