Update README.md

Author: kmacmcfarlane

README.md

@@ -13,3 +13,13 @@ To use the application, first build with `make`, then execute the application pr
 
 `make`
 `./bin/csv-2-postgresql test2.csv postgres://postgres:hello@localhost/test?sslmode=disable`
+
+# Design
+
+* main package (csv-2-postgresql) defines both the entry point to the application and the main interfaces (Parser and DatabaseWriter).
+  * These interfaces have implementations using 3rd party packages for handling the CSV and Postgresql part of their operation.
+  * This helps relieve the dependencies that must be brought into the main program, decreasing coupling.
+* The schema package defines the domain model (which is simply the schema of the CSV file for this problem space).
+* Both the CSV parser and Postgresql DB adapter use private helper methods to determine the types best suited for the data and convert to types compatible with the database.
+* Unit tests cover all the business logic in the CSV parser and Postgresql database adapter.
+* I neglected to use vendoring for this project to keep things simple, the latest versions of build and test dependencies are installed using the Makefile automatically when building or testing.