Address comments

.devcontainer/post-create-command.sh

@@ -7,6 +7,10 @@ if ! git remote | grep -q "fork"; then
     git remote add fork https://github.com/${GIT_USER}/flask
 fi
 
+# Create and activate a virtualenv
+python3 -m venv .venv
+. .venv/bin/activate
+
 # Upgrade pip and setuptools
 python -m pip install --upgrade pip setuptools