better readme

Author: QuentinGab

README.md

@@ -1,4 +1,3 @@
-
 # Manage invoices in your Laravel App
 
 [![Latest Version on Packagist](https://img.shields.io/packagist/v/finller/laravel-invoices.svg?style=flat-square)](https://packagist.org/packages/finller/laravel-invoices)
@@ -80,10 +79,47 @@ return [
 
 ## Usage
 
+## Store an invoice in your database
+
+An invoice is just a model with InvoiceItem relationships, so you can create an invoice just like that:
+
 ```php
 use Finller\Invoice\Invoice;
+$invoice = new Invoice();
+$invoice->save();
+
+$invoice->items()->saveMany([
+    new InvoiceItem(),
+    new InvoiceItem(),
+]);
+```
+
+## Generate unique serial numbers automatically
+
+This package provid an easy way to generate explicite serial number like "INV-0001" in a safe and automatic way.
 
+You can configure the format of your serial number in the config file. The default format is `PPYYCCCC``(see config to understand the meaning of each letters).
+
+Each time you create a new invoice, and if `invoices.serial_number.auto_generate` is set to `true`, the invoice will be given a unique serial number.
+
+Serial number are generated one after the other, the new generated serial number is based on the `latest` one available.
+To determine which is the `latest` serial number you can extends `Finller\Invoice\Invoice`
+and override the `getLatestSerialNumber` method.
+By default the lastest invoice is queried like that `static::query()->latest('serial_number')->first();`.
+
+## Managing multiple prefix and multiple series
+
+In more complex app, you might need to have different prefix and/or series for your invoices.
+
+For example, you might want to define a serie for each of your user and having serial numbers looking like: INV0001-00X where 1 is the id of the user.
+
+When creating an invoice, you can define the prefix and the serie on the fly like that;
+
+```php
+use Finller\Invoice\Invoice;
 $invoice = new Invoice();
+$invoice->prefix = "SPECIAL";
+$invoice->serie = $buyer_id;
 $invoice->save();
 ```
 
@@ -107,8 +143,8 @@ Please review [our security policy](../../security/policy) on how to report secu
 
 ## Credits
 
-- [Quentin Gabriele](https://github.com/QuentinGab)
-- [All Contributors](../../contributors)
+-   [Quentin Gabriele](https://github.com/QuentinGab)
+-   [All Contributors](../../contributors)
 
 ## License