rewrite tutorial docs and example

examples/tutorial/flaskr/schema.sql

@@ -0,0 +1,20 @@
+-- Initialize the database.
+-- Drop any existing data and create empty tables.
+
+DROP TABLE IF EXISTS user;
+DROP TABLE IF EXISTS post;
+
+CREATE TABLE user (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  username TEXT UNIQUE NOT NULL,
+  password TEXT NOT NULL
+);
+
+CREATE TABLE post (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  author_id INTEGER NOT NULL,
+  created TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  title TEXT NOT NULL,
+  body TEXT NOT NULL,
+  FOREIGN KEY (author_id) REFERENCES user (id)
+);