message: Add docker layer caching for cross ci tasks
  The `cross` CI jobs uses docker. Cache the docker images across builds.
diff: @@ -32,6 +32,8 @@ jobs:
  override: true
  - name: Cache
  uses: Swatinem/rust-cache@v1
  + - name: Docker Cache
  + uses: satackey/action-docker-layer-caching@v0.0.11
  - name: Checkout
  uses: actions/checkout@v2
  - name: Build
  