ci: add checksum for release binary (#1482)

.github/workflows/release.yml

@@ -82,6 +82,14 @@ jobs:
 
       - name: Strip release binary
         run: strip "target/${{ matrix.target }}/release/zellij"
+
+      - name: Create checksum
+        id: make-checksum
+        working-directory: ./target/${{ matrix.target }}/release
+        run: |
+          name="zellij-${{ matrix.target }}.sha256sum"
+          sha256sum "zellij" > "${name}"
+          echo "::set-output name=name::${name}"
         
       - name: Tar release
         id: make-artifact
@@ -90,6 +98,7 @@ jobs:
           name="zellij-${{ matrix.target }}.tar.gz"
           tar cvzf "${name}" "zellij"
           echo "::set-output name=name::${name}"
+
       - name: Upload release archive
         uses: actions/upload-release-asset@v1.0.2
         env:
@@ -100,6 +109,16 @@ jobs:
           asset_name: zellij-${{matrix.target}}.tar.gz
           asset_content_type: application/octet-stream
 
+      - name: Upload checksum
+        uses: actions/upload-release-asset@v1.0.2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          upload_url: ${{ needs.create-release.outputs.upload_url }} 
+          asset_path: ./target/${{ matrix.target }}/release/${{ steps.make-checksum.outputs.name }}
+          asset_name: zellij-${{matrix.target}}.sha256sum
+          asset_content_type: text/plain
+
   create-release:
     runs-on: ubuntu-latest
     outputs: