Add release workflow

Author: Morganov

.github/workflows/release.yml

@@ -0,0 +1,41 @@
+name: Release from master
+
+on:
+  push:
+    branches: [ master ]
+  
+  workflow_dispatch:
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - name: Compute tag name
+        id: compute-tag
+        run: |
+          echo "Computing next tag number"
+          LASTPATCH=$(git describe --tags | cut -d- -f1 | cut -d. -f3)
+          PATCH=$(($LASTPATCH+1))
+          echo "New tag name: 2.1.${PATCH}"
+          echo "::set-output name=tagname::2.1.${PATCH}"
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.7
+          bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+      
+      - name: Build release assets
+        run: bundle exec rake book:build
+        
+      - name: Create Release
+        uses: ncipollo/release-action@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          tag: ${{ steps.compute-tag.outputs.tagname }}
+          comit: master
+          artifacts: './progit.epub,./progit.pdf,./progit.html'