chore: add release workflow

.github/workflows/release.yml

@@ -0,0 +1,32 @@
+name: Hexpm Release
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  publish:
+    name: Publish
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Elixir
+      uses: erlef/setup-elixir@v1
+      with:
+        elixir-version: '1.13'
+        otp-version: '24.3'
+    - name: Restore dependencies cache
+      uses: actions/cache@v2
+      with:
+        path: deps
+        key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-
+    - name: Install dependencies
+      run: |
+        mix local.rebar --force
+        mix local.hex --force
+        mix deps.get
+    - name: Run Hex Publish
+      run: mix hex.publish --yes
+      env:
+        HEX_API_KEY: ${{ secrets.HEX_API_KEY }}