Install docs dependencies in a virtual env

.gitignore

@@ -49,4 +49,5 @@ Thumbs.db
 *.sdf
 *.opensdf
 build
+.venv/
 .vscode/

README.md

@@ -65,8 +65,12 @@ You may also need to set `BOOST_ROOT` if CMake cannot find Boost.
 The documentation is built using [Doxygen](http://www.stack.nl/~dimitri/doxygen/), [Breathe](https://breathe.readthedocs.io/en/latest/) and [Sphinx](http://www.sphinx-doc.org/en/stable/). Install Doxygen and Python and make sure they're accessible from your `PATH`, then run:
 
 ```
+py -m venv .venv
+.venv\Scripts\activate
 pip install -r docs/requirements.txt
 sphinx-build -b html docs build/docs/html
 ```
 
+If running on Linux, replace `.venv\Scripts\activate` with `.venv/bin/activate`.
+
 Alternatively, you can use Docker to avoid changing your development environment, by running `docker run -it --rm -v ${PWD}/docs:/docs/docs -v ${PWD}/build:/docs/build -v ${PWD}/include:/docs/include sphinxdoc/sphinx:7.3.7 bash` to obtain a shell that you can use to run `apt-get update && apt-get install -y doxygen` and then the two commands above.