Merge pull request #2 from mrl5/docs-example

docs(README): document example

Author: porsager

README.md

@@ -9,3 +9,78 @@ A simple forwards only migration solution for [postgres.js](https://github.com/p
 It expects a [postgres.js sql]() database object to run migrations with.
 
 ## `Example`
+
+1. Create `migrations` directory with following structure
+```
+.
+└── migrations
+    ├── 00001_initial
+    │   └── index.sql
+    ├── 00002_update
+    │   └── index.js
+    └── 00003_delete
+        └── index.sql
+```
+Note that migration folder name expects 5 digits. This is very important
+detail.
+
+2. Create actual migrations. Note that it can be either in SQL or JS syntax
+```sql
+create table test (
+  a text,
+  b int
+)
+```
+```js
+export default async function(sql) {
+  await sql`
+    alter table test add column c timestamp with time zone
+  `
+
+  await sql`
+    insert into test (a, b, c) values ('hello', 9, ${ new Date() })
+  `
+}
+```
+
+3. Create your `migrate.js` script:
+```js
+import shift from 'postgres-shift';
+import postgres from 'postgres';
+import { fileURLToPath } from 'url';
+
+const {
+    DB_HOST,
+    DB_PORT,
+    DB_NAME,
+    ADMIN_DB_USER,
+    ADMIN_DB_PASSWORD,
+} = process.env;
+
+export const sql = postgres({
+    host: DB_HOST,
+    port: Number(DB_PORT),
+    database: DB_NAME,
+    user: ADMIN_DB_USER,
+    pass: ADMIN_DB_PASSWORD,
+    idle_timeout: 1,
+});
+
+shift({
+    sql,
+    path: fileURLToPath(new URL('migrations', import.meta.url)),
+    before: ({ migration_id, name }) => {
+        console.log('Migrating', migration_id, name);
+    },
+})
+    .then(() => console.log('All good'))
+    .catch((err) => {
+        console.error('Failed', err);
+        process.exit(1);
+    });
+```
+
+4. Run it with
+```console
+node ./migrate.js
+```