Add ReadTheDocs CI (#5456)

.github/workflows/docs.yml

+name: ReadTheDocs CI
+
+on:
+  push:
+    branches:
+    - master
+    - release/*
+    paths:
+    - 'docs/**'
+    - '.github/workflows/docs.yml'
+  pull_request:
+    paths:
+    - 'docs/**'
+    - '.github/workflows/docs.yml'
+
+jobs:
+
+  build-docs:
+    name: Build ReadTheDocs
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - uses: actions/setup-python@v2
+      with:
+        python-version: '3.x'
+    - name: Build
+      run: |
+        sudo apt update
+        sudo apt install python3-pip python3-setuptools
+        # GitHub CI installs pip3 and setuptools outside the path.
+        # Update the path to include them and run.
+        PATH=/home/runner/.local/bin:$PATH pip3 install --user -r ./docs/requirements.txt
+        cd ./docs && PATH=/home/runner/.local/bin:$PATH SPHINXOPTS="-W" make html

docs/source/conf.py

@@ -56,7 +56,7 @@ exclude_patterns = []
 # a list of builtin themes.
 #
 html_theme = 'default'
-html_logo = 'logo_espressif.png'
+html_logo = '_static/logo_espressif.png'
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,