doc: add note for pip requirement in system env

docs/docs/configuration.md

@@ -107,6 +107,10 @@ Defaults to one of the following directories:
 Create a new virtual environment if one doesn't already exist.
 Defaults to `true`.
 
+!!!note:
+        When setting this configuration to `false`, the Python environment used must have `pip` 
+        installed and available.
+
 ### `virtualenvs.in-project`: boolean
 
 Create the virtualenv inside the project's root directory.