docs: readthedocs.org support

.woodpecker.yml

@@ -17,3 +17,7 @@ pipeline:
     image: python
       - pip install -U platformio
       - pio check -e esp8266 -e esp32 --skip-packages --severity medium --severity high --pattern 'src' --pattern 'lib/Figments' --fail-on-defect high
+  docs:
+    image: python
+      - pip install -U breathe sphinx
+      - cd docs && sphinx