[doc] add basic README info on pipenv

Pipenv is a recent python tool, so add a bit of documentation in the
readme for users.

README.markdown

@@ -6,6 +6,22 @@ power usage of application.
 This is a python rewrite of the original code developed for the Argo project
 two years ago.
 
+## Requirements
+
+Python dependencies are managed by `pipenv`. You should be able to get the code
+running simply with:
+
+> pipenv install
+
+And entering the resulting virtual environment with `pipenv shell`.
+
+The NRM code only supports _argo-containers_ for now, so you need to install
+the our container piece on the system for now.
+
+## Basic Usage
+
+Launch the `daemon`, and use `cmd` to interact with it.
+
 ## Additional Info
 
 | **Systemwide Power Management with Argo**