Update release workflow to on dispatch and add notes about releasing

.github/workflows/release.yml

@@ -0,0 +1,42 @@
+name: Release
+
+on: workflow_dispatch
+
+jobs:
+  release:
+    name: Build + Publish
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Get Version
+      id: gv
+      run: |
+        echo "::set-output name=ver::$(grep VERSION lib/vmfloaty/version.rb |rev |cut -d "'" -f2 |rev)"
+
+    - name: Tag Release
+      uses: ncipollo/release-action@v1
+      with:
+        tag: ${{ steps.gv.outputs.ver }}
+        token: ${{ secrets.GITHUB_TOKEN }}
+        draft: false
+        prerelease: false
+        generateReleaseNotes: true
+
+    - name: Set up Ruby 2.7
+      uses: actions/setup-ruby@v1
+      with:
+        version: 2.7.x
+
+    - name: Build gem
+      run: gem build *.gemspec
+
+    - name: Publish gem
+      run: |
+        mkdir -p $HOME/.gem
+        touch $HOME/.gem/credentials
+        chmod 0600 $HOME/.gem/credentials
+        printf -- "---\n:rubygems_api_key: ${GEM_HOST_API_KEY}\n" > $HOME/.gem/credentials
+        gem push *.gem
+      env:
+        GEM_HOST_API_KEY: ${{secrets.RUBYGEMS_AUTH_TOKEN}}