Add a new database table for subjects

We need to store basic information about the infrasture we store results
for. Create a table called `subjects` for this purpose. This partially
addresses #29.

.gitignore

@@ -7,3 +7,6 @@ configs/config.yaml
 # Terraform
 terraform/.terraform*
 terraform/terraform.*
+
+# Ignore the golang-migrate/migrate binary
+migrate

README.md

@@ -62,6 +62,11 @@ $ terraform apply
 
 Cleanup the resources using `terraform destroy`.
 
+## Migrations
+
+Please refer to the [migrations documentation](./migrations/README.md) for
+instructions on creating and managing database migrations.
+
 ## gRPC API
 
 This API is marked as **EXPERIMENTAL** and may change in backwards incompatible

migrations/000001_create_subject_table.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS subjects;

migrations/000001_create_subject_table.up.sql

@@ -0,0 +1,5 @@
+CREATE TABLE IF NOT EXISTS subjects (
+   id serial PRIMARY KEY,
+   name VARCHAR(255),
+   type VARCHAR(50)
+);

migrations/README.md

@@ -1,6 +1,31 @@
 # Database Migrations
 
 This folder contains database migrations for the compliance service using
-[golang-migrate/migrate](https://github.com/golang-migrate/migrate). Please
-refer to migrate
-[documentation](https://github.com/golang-migrate/migrate/tree/master/cmd/migrate).
+[golang-migrate/migrate](https://github.com/golang-migrate/migrate).
+
+This project requires using the `migrate` CLI to change the database schema and
+to add new migrations. Please refer to the
+[documentation](https://github.com/golang-migrate/migrate/tree/master/cmd/migrate)
+for installation instructions.
+
+## Examples
+
+These examples assume you have a PostgreSQL server accessible with a database
+named `compliance`, and you've properly
+[escaped](https://github.com/golang-migrate/migrate#database-urls) the database
+password. You can refer to the deployment documentation in the
+[README.md](../README.md) for instructions on using terraform to deploy a
+database using AWS RDS.
+
+Apply all migrations:
+
+```console
+$ POSTGRESQL_URL="postgres://$USER:$PASSWORD@$DATABASE_ENDPOINT/compliance
+$ ./migrate -database $POSTGRESQL_URL -path migrations up
+```
+
+Apply all down migrations:
+
+```console
+$ ./migrate -database $POSTGRESQL_URL -path migrations down
+```