Add service metadata file (#22)

Adds a `metadata.yaml` file to the root of the repository to describe the service's metadata and versions.

Author: RedbackThomson

metadata.yaml

@@ -0,0 +1,8 @@
+service:
+  full_name: "Amazon Relational Database Service"
+  short_name: "RDS"
+  link: "https://aws.amazon.com/rds/"
+  documentation: "https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/index.html"
+api_versions:
+  - api_version: v1alpha1
+    status: available