Prepare workflow to publish gh-pages

.github/workflows/phono3py-pytest-conda-mkl.yml

@@ -3,6 +3,7 @@ name: Pytest with mkl
 on:
   push:
     branches-ignore:
+    - publish-gh-pages
     - master
     - rc
 

.github/workflows/phono3py-pytest-conda.yml

@@ -3,6 +3,7 @@ name: Pytest with openblas
 on:
   push:
     branches-ignore:
+    - publish-gh-pages
     - master
     - rc
 

.github/workflows/publish-gh-pages.yml

@@ -0,0 +1,41 @@
+name: publish phono3py gh-pages
+
+on:
+  push:
+    branches: [publish-gh-pages]
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash -l {0}
+    strategy:
+      matrix:
+        python-version: ["3.9"]
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: conda-incubator/setup-miniconda@v2
+      with:
+        auto-update-conda: true
+        channels: conda-forge
+        channel-priority: strict
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        conda activate test
+        conda install --yes -c conda-forge python=${{ matrix.python-version }}
+        conda install --yes -c conda-forge sphinx-book-theme linkify-it-py "myst-parser=0.17.2" sphinxcontrib-bibtex
+    - name: Build
+      run: |
+        conda activate test
+        sphinx-build doc docs_build
+
+    - name: Deploy docs at develop branch
+      if: ${{ github.ref == 'refs/heads/publish-gh-pages' }}
+      uses: peaceiris/actions-gh-pages@v3
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        publish_dir: ./docs_build
+        # deploy_key: ${{ secrets.ACTIONS_DEPLOY_KEY }}