Add architecture diagram and readme

documentation/architecture/README.md

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+# NAD Collaboration Hub Architecture
+
+### Entry Points
+
+Users can work with the NAD Collaboration Hub by way of:
+
+- **Flask Web Server**: Primary interface for web-based interactions for Data
+  Producers and NAD Administrator.
+- **CLI**: Command line interface allowing NAD Administrator to perform
+  administrative tasks.
+
+### Application Core
+
+Logic concerning business rules, data validation and profiling, and other
+application concerns. The core is unaware of how its entry points and its
+infrastructure dependencies are implemented.
+
+### Infrastructure Dependencies
+
+The current remote development environment uses [services provided by cloud.gov](https://cloud.gov/docs/services/intro/).
+
+- **Object Storage**: Storage for datasets submitted by users, via
+  [S3](https://cloud.gov/docs/services/s3/).
+- **Relational Database**: Persistence for application data and data validation
+  reports, via [RDS PostgreSQL database](https://cloud.gov/docs/services/relational-database/).
+- **Task Queue Broker**: Manages queue of data validation tasks for Celery, via
+  [AWS Elasticache Redis](https://cloud.gov/docs/services/aws-elasticache/).