bpo-34324: Doc README wrong directory name for venv (GH-8650)

In the documentation, the `env` directory is specified when we execute
the `make venv` command. But in the code, `make venv` will create the
virtualenv inside the `venv` directory (defined by `VENVDIR`)

Doc/README.rst

@@ -33,7 +33,7 @@ To get started on UNIX, you can create a virtual environment with the command ::
   make venv
 
 That will install all the tools necessary to build the documentation. Assuming
-the virtual environment was created in the ``env`` directory (the default;
+the virtual environment was created in the ``venv`` directory (the default;
 configurable with the VENVDIR variable), you can run the following command to
 build the HTML output files::