Please consider setting pragma WAL in your introductory documentation (…

…WiseLibs#831)

The performance difference can be several orders of magnitude on even simple tables, and most users won't think to go looking for this.

I've included lines that clarify, and link to your existing documentation on the topic.

Thank you for an excellent tool.

README.md

@@ -43,11 +43,18 @@ const row = db.prepare('SELECT * FROM users WHERE id = ?').get(userId);
 console.log(row.firstName, row.lastName, row.email);
 ```
 
+Though not required, [it is generally important to set the WAL pragma for performance reasons](https://github.com/WiseLibs/better-sqlite3/blob/master/docs/performance.md).
+
+```js
+db.pragma('journal_mode = WAL');
+```
+
 ##### In ES6 module notation:
 
 ```js
 import Database from 'better-sqlite3';
 const db = new Database('foobar.db', options);
+db.pragma('journal_mode = WAL');
 ```
 
 ## Why should I use this instead of [node-sqlite3](https://github.com/mapbox/node-sqlite3)?