Add GHA to publish documentation

Author: klmr

.github/workflows/build.yaml

@@ -39,3 +39,34 @@ jobs:
           git add --force NAMESPACE man
           git commit -m 'Create a development build'
           git push --force origin build
+
+  docs:
+    name: Publish documentation
+    runs-on: ubuntu-latest
+    needs: build
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: r-lib/actions/setup-r@v2
+
+      - uses: r-lib/actions/setup-r-dependencies@v2
+        with:
+          dependencies: NA
+          extra-packages: any::pkgdown
+
+      - name: Build documentation
+        run: |
+          git checkout build
+          make site
+
+      - name: Publish documentation
+        run: |
+          git config user.name klmr
+          git config user.email klmr@users.noreply.github.com
+          git remote set-url --push origin https://klmr:$GITHUB_TOKEN@github.com/klmr/box.git
+          git branch -D site 2>/dev/null || :
+          git checkout -b site
+          git add --force docs
+          git commit -m 'Build documentation'
+          git push --force origin site