add support for reading database url from password

05-example-web-application/api-node/src/db.js

@@ -1,7 +1,13 @@
+const fs = require('fs');
+
 const { Pool } = require('pg');
 
+databaseUrl =
+  process.env.DATABASE_URL ||
+  fs.readFileSync(process.env.DATABASE_URL_FILE, 'utf8');
+
 const pool = new Pool({
-  connectionString: process.env.DATABASE_URL,
+  connectionString: databaseUrl,
 });
 
 // the pool will emit an error on behalf of any idle clients