simplify config, update guide

CONTRIBUTING.rst

@@ -70,24 +70,18 @@ Include the following in your patch:
 First time setup using GitHub Codespaces
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-`GitHub Codespaces`_ allow you to create an instant and dedicated
-development environment. Codespaces open by default in Visual Studio
-Code for the Web, but also work in the desktop app. Codespaces created
-from Flask are configured with a `devcontainer`_ that installs required
-dependencies for you.
+`GitHub Codespaces`_ creates a development environment that is already set up for the
+project. By default it opens in Visual Studio Code for the Web, but this can
+be changed in your GitHub profile settings to use Visual Studio Code or JetBrains
+PyCharm on your local computer.
 
 -   Make sure you have a `GitHub account`_.
--   From the Flask repository page, click the green "Code" button and
-    then "Create codespace on main".
--   Wait for the codespace to load and the ``postCreateCommand`` to
-    finish running.
--   Run the following command to activate the python virtualenv.
-
-    .. code-block:: text
-
-        $ . .venv/bin/activate
-
--   Checkout a branch and `start coding`_.
+-   From the project's repository page, click the green "Code" button and then "Create
+    codespace on main".
+-   The codespace will be set up, then Visual Studio Code will open. However, you'll
+    need to wait a bit longer for the Python extension to be installed. You'll know it's
+    ready when the terminal at the bottom shows that the virtualenv was activated.
+-   Check out a branch and `start coding`_.
 
 .. _GitHub Codespaces: https://docs.github.com/en/codespaces
 .. _devcontainer: https://docs.github.com/en/codespaces/setting-up-your-project-for-codespaces/adding-a-dev-container-configuration/introduction-to-dev-containers