doc: install numpy in virtualenv to run test

doc/_readme/scripts/run.sh

@@ -1,7 +1,16 @@
 #!/bin/bash
 cd ./doc/_readme/ || exit 1
 llgo build -v ./...
-pip3 install --user numpy
+
+python3 -m venv .venv
+# shellcheck source=/dev/null
+source .venv/bin/activate
+pip3 install numpy
+
+PYTHONPATH=""
+PYTHONPATH=$(python -c "import sys; print(':'.join(sys.path))")
+export PYTHONPATH
+
 for dir in ./*/; do
   if grep -q "func main()" "$dir"/*.go 2>/dev/null; then
     echo "Running examples in $dir"