fix: Output Sphinx docs to RTD-required directory

Read the Docs requires HTML output to be written to
$READTHEDOCS_OUTPUT/html/ when using custom build commands.

Changes:
- Add mkdir -p $READTHEDOCS_OUTPUT/html/ before build
- Change sphinx-build output from docs/_build/html to $READTHEDOCS_OUTPUT/html

This fixes the "No HTML content found" error on RTD builds.

Ref: https://docs.readthedocs.com/platform/stable/build-customization.html#where-to-put-files

Author: oberstet

readthedocs.yml

@@ -9,5 +9,7 @@ build:
     - bash .github/scripts/rtd-download-artifacts.sh
     # Install package with all extras needed for docs
     - pip install -e ".[dev,twisted,compress,serialization,encryption,scram]"
-    # Build Sphinx documentation
-    - cd docs && sphinx-build -b html . _build/html
+    # Create RTD output directory (required by RTD)
+    - mkdir -p $READTHEDOCS_OUTPUT/html/
+    # Build Sphinx documentation to RTD output directory
+    - cd docs && sphinx-build -b html . $READTHEDOCS_OUTPUT/html