readme: use newer sphinx for local docs building

README.md

@@ -170,9 +170,11 @@ Chimney documentation is available at https://chimney.readthedocs.io.
 For building documentation locally you can use Docker:
 
 ```bash
-docker run --rm -v "$PWD/docs:/docs" sphinxdoc/sphinx:3.2.1 bash -c "pip install sphinx-rtd-theme && make html"
+docker run --rm -v "$PWD/docs:/docs" sphinxdoc/sphinx:5.3.0 bash -c "pip install sphinx-rtd-theme && make html"
 ```
 
+It will build the docs in the `./docs/build/html/` directory.
+
 ## Thanks
 
 Thanks to [JProfiler (Java profiler)](https://www.ej-technologies.com/products/jprofiler/overview.html)