Add Github Action cache example into README.md

README.md

@@ -81,7 +81,7 @@ To use Dialyzer in CI, you must be aware of several things:
 2) The PLT should be cached using the CI caching system
 3) The PLT will need to be rebuilt whenever adding a new Erlang or Elixir version to build matrix
 
-Using Travis, this would look like:
+### Travis
 
 `.travis.yml`
 ```markdown
@@ -101,6 +101,43 @@ cache:
     - priv/plts
 ```
 
+### Github Actions
+
+`dialyzer.yml`
+```yaml
+...
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Elixir
+        id: beam
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: "1.12.3" # Define the elixir version
+          otp-version: "24.1" # Define the OTP version
+
+      # Don't cache PLTs based on mix.lock hash, as Dialyzer can incrementally update even old ones
+      # Cache key based on Elixir & Erlang version (also usefull when running in matrix)
+      - name: Restore PLT cache
+        uses: actions/cache@v2
+        id: plt_cache
+        with:
+          key: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-plt
+          restore-keys: |
+            ${{ runner.os }}-${{ steps.beam.outputs.elixir-version }}-${{ steps.beam.outputs.otp-version }}-plt
+          path: |
+            priv/plts
+
+      # Create PLTs if no cache was found
+      - name: Create PLTs
+        if: steps.plt_cache.outputs.cache-hit != 'true'
+        run: mix dialyzer --plt
+
+      - name: Run dialyzer
+        run: mix dialyzer
+
+```
+
 `mix.exs`
 ```elixir
 def project do