[PSM tests] Troubleshoot Ubuntu venv issue (#32786)

tools/run_tests/xds_k8s_test_driver/README.md

@@ -30,6 +30,11 @@ changes to this codebase at the moment.
 
 `kubectl` can be installed via `gcloud components install kubectl`, or system package manager: https://kubernetes.io/docs/tasks/tools/#kubectl
 
+Python3 venv tool may need to be installed from APT on some Ubuntu systems:
+```shell
+sudo apt-get install python3-venv
+```
+
 ##### Getting Started
 
 1. If you haven't, [initialize](https://cloud.google.com/sdk/docs/install-sdk) gcloud SDK
@@ -174,7 +179,7 @@ export KUBE_CONTEXT="$(kubectl config current-context)"
 
 ```shell
 # Create python virtual environment
-python3.7 -m venv venv
+python3 -m venv venv
 
 # Activate virtual environment
 . ./venv/bin/activate