add workflow to test PR builds fine

(cherry picked from commit 3c3888f7ad)

.github/workflows/build.yml

@@ -0,0 +1,32 @@
+name: Build
+
+on:
+  pull_request:
+    branches:
+      - master
+      - exampleSite
+  workflow_dispatch:
+    # manual run
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Git checkout
+        uses: actions/checkout@v2
+        with:
+          ref: exampleSite
+
+      - name: Get Theme
+        run: git submodule update --init --recursive
+
+      - name: Update theme to Latest commit
+        run: git submodule update --remote --merge
+
+      - name: Setup hugo
+        uses: peaceiris/actions-hugo@v2
+        with:
+          hugo-version: 'latest'
+
+      - name: Build
+        run: hugo --buildDrafts --gc --verbose --minify