add virtualenv page

pages/common/virtualenv.md

@@ -0,0 +1,16 @@
+# virtualenv
+
+> Create virtual isolated Python environments
+
+- Create a new environment
+
+`virtualenv {{path/to/venv}}`
+
+- Start (select) the environment
+
+`source {{path/to/venv}}/bin/activate`
+
+- Stop the environment
+
+`deactivate`
+