nit(installation): note requirement to activate virtual env

Signed-off-by: Cameron Smith <cameron.ray.smith@gmail.com>

nbs/guides/installation.qmd

@@ -49,6 +49,7 @@ version, create a virtual environment, and install pyrovelocity from a blank dir
 echo "3.10" > .python-version
 uv python install
 uv venv -p 3.10
+source .venv/bin/activate
 uv pip install pyrovelocity
 ```