add database schema and update docker-compose for initialization

db/sql/01_schema.sql

@@ -0,0 +1,15 @@
+CREATE SCHEMA IF NOT EXISTS ethnograph;
+
+CREATE TABLE IF NOT EXISTS ethnograph.users (
+    id SERIAL PRIMARY KEY,
+    username VARCHAR(255) UNIQUE NOT NULL,
+    created_utc TIMESTAMP NOT NULL,
+    karma INTEGER
+);
+
+CREATE TABLE IF NOT EXISTS ethnograph.posts (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER REFERENCES ethnograph.users(id),
+    content TEXT NOT NULL,
+    created_utc TIMESTAMP NOT NULL
+);