Update the README

Now that there is only a single dependency configuration we need to
update the README's directions for updating Python dependencies.

Author: mcdonnnj

README.md

@@ -59,18 +59,15 @@ docker compose down
 
 ## How to update Python dependencies ##
 
-The Python dependencies are maintained using a
-[Pipenv](https://github.com/pypa/pipenv) configuration for each
-supported Python version. Changes to requirements should be made to
-the respective `src/py<Python version>/Pipfile`. More information
-about the `Pipfile` format can be found in the [`pipenv`
-documentation](https://pipenv.pypa.io/en/latest/pipfile.html#example-pipfile).
-The accompanying `Pipfile.lock` files contain the specific dependency
-versions that will be installed. These files can be updated like so
-(using the Python 3.9 configuration as an example):
+The Lambda's Python dependencies are maintained using a [Pipenv](https://github.com/pypa/pipenv)
+configuration. Changes to requirements should be made to the `Pipfile` located at
+`build/Pipfile`. More information about the `Pipfile` format can be found in the
+[`pipenv` documentation](https://pipenv.pypa.io/en/latest/pipfile.html#example-pipfile).
+The accompanying `Pipfile.lock` file contains the specific dependency versions
+that will be installed. This file is updated automatically like so:
 
 ```console
-cd src/py3.9
+cd build
 pipenv lock
 ```