Update README with additional info

- Project description
- Add submodule related info
- Add scriptz README reference
- Reformat Installation section

README.md

@@ -3,11 +3,32 @@
 
 [![Build Status](https://travis-ci.org/dod-ccpo/atst.svg?branch=master)](https://travis-ci.org/dod-ccpo/atst)
 
+## Description
+
+This is the main user-facing web application for the ATAT stack. All end-user
+requests are handled by ATST, with it making backend calls to various
+microservices when appropriate.
+
 ## Installation
 
+See the [scriptz](https://github.com/dod-ccpo/scriptz) repository for the shared 
+requirements and guidelines for all ATAT applications.
+
+This project contains git submodules. Here is an example clone command that will 
+automatically initialize and update those modules:
+`git clone --recurse-submodules git@github.com:dod-ccpo/atst.git`
+
+This application uses Pipenv to manage Python dependencies and a virtual
+environment. Instead of the classic `requirements.txt` file, pipenv uses a 
+Pipfile and Pipfile.lock, making it more similar to other modern package managers 
+like yarn or mix.
+
+To perform the installation, run the setup script:
+
     script/setup
 
-The setup script installs pipenv, which is what this application uses to manage its dependences and virtualenv. Instead of the classic `requirements.txt` file, pipenv uses a Pipfile and Pipfile.lock, making it more similar to other modern package managers like yarn or mix.
+The setup script creates the virtual environment, and then calls script/bootstrap 
+to install all of the Python and Node dependencies.
 
 To enter the virtualenv manually (a la `source .venv/bin/activate`):
 
@@ -25,7 +46,7 @@ To start the app locally in the foreground and watch for changes:
 
 ## Testing
 
-To run all linting and tests:
+To run lint, static analysis, and unit tests:
 
     script/test