Problem: missing packaging of unreal demo project (fix #86) (#10)

Solution: add release github action

.github/workflows/release.yml

@@ -0,0 +1,50 @@
+name: Release
+
+on:
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - README.md
+    tags:
+      - "v*.*.*"  
+  pull_request:
+    paths-ignore:
+      - README.md
+
+jobs:
+  linux-build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          submodules: recursive
+
+      - name: Prepare Plugin
+        run: |
+          cd Plugins/play-unreal-plugin && make 
+
+      - name: Package For Windows,Mac
+        run: |
+          FILENAME="CronosPlayDemo.zip"
+          cd ..
+          zip -r ${FILENAME} play-unreal-demo -x "play-unreal-demo/.git/*" "play-unreal-demo/.git/*" "play-unreal-demo/Plugins/play-unreal-plugin/.git/*"  "play-unreal-demo/Plugins/play-unreal-plugin/.github/*" "play-unreal-demo/Plugins/play-unreal-plugin/install/*"
+          mv ${FILENAME} play-unreal-demo
+          cd play-unreal-demo
+          sha256sum ${FILENAME} > "checksums.txt"
+          echo "release_file=${FILENAME}" >> $GITHUB_ENV
+          echo "checksum_file=checksums.txt" >> $GITHUB_ENV
+          
+
+      - name: Upload binaries and bindings to Release
+        uses: softprops/action-gh-release@v1
+        if: github.event_name == 'push' && contains(github.ref, 'refs/tags/')
+        with:
+          draft: true
+          files: |
+            ${{ env.release_file }}
+            ${{ env.checksum_file }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}            
+