Update current.sql with an example table

Would love to have an example table in the `current.sql` to show how powerful this setup really is.

The intention here is to show the `graphile-migrate` in action for the new users.

Author: eleijonmarck

@app/db/migrations/current.sql

@@ -1 +1,32 @@
 -- Enter migration here
+
+/*
+example of a table that could be created after setup complete
+
+- uncomment the statements below
+- save the file and graphile-migrate will update the schema into database automagically
+*/
+
+-- CREATE TYPE app_public.post_topic AS enum (
+--   'discussion',
+--   'inspiration',
+--   'help',
+--   'showcase'
+-- );
+
+-- CREATE TABLE IF NOT EXISTS app_public.post (
+--   id               SERIAL PRIMARY KEY,
+--   author_id        INTEGER NOT NULL REFERENCES app_public.users(id),
+--   headline         TEXT NOT NULL CHECK (char_length(headline) < 280),
+--   body             TEXT,
+--   topic            app_public.post_topic,
+--   created_at       TIMESTAMP default NOW()
+-- );
+
+-- COMMENT ON TABLE APP_PUBLIC.POST IS 'A forum post written by a user.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.ID IS 'The primary key for the post.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.HEADLINE IS 'The title written by the user.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.AUTHOR_ID IS 'The id of the author user.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.TOPIC IS 'The topic this has been posted in.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.BODY IS 'The main body text of our post.';
+-- COMMENT ON COLUMN APP_PUBLIC.POST.CREATED_AT IS 'The time this post was created.';