prepare for release + added an example in the doc

CHANGELOG.md

@@ -2,7 +2,12 @@
 
 ## Unreleased
 
-Nothing
+ * nothing
+
+## 4.0.1 (2020-07-30)
+
+ * upgrade to `janephp/open-api` 6.0
+ * fixed boolean query parameters serialization
 
 ## 4.0.0 (2020-05-14)
 
@@ -30,7 +35,7 @@ Nothing
    * several new "report" endpoints
    * support for `rounded_hours` in the `TimeEntry` model
 
-## 2.1.0
+## 2.1.0 (2020-01-14)
 
  * updated the OpenAPI definition file
  * added the "company update" endpoint

doc/index.md

@@ -44,6 +44,8 @@ $clients = $harvestClient->listClients([
 ])->getClients();
 ```
 
+## Available operations
+
 Instead of `listClients()`, you can use all of these methods:
 
  * Clients:
@@ -174,6 +176,24 @@ Instead of `listClients()`, you can use all of these methods:
    * `retrieveCostRate()`
    * `listActiveProjectAssignments()`
 
+## Examples
+
+### Create an invoice
+
+```php
+use JoliCode\Harvest\ClientFactory;
+
+$harvestClient = ClientFactory::create(
+  $accessToken,
+  $harvestAccountId
+);
+
+$payload = new \JoliCode\Harvest\Api\Model\InvoicesPostBody();
+$payload->setClientId(123456);
+$payload->setSubject('test invoice, please delete it');
+$invoice = $client->createInvoice($payload);
+```
+
 ## Bypassing the incomplete API specification
 
 Harvest's API does not have an officially supported OpenAPI specification. This library is automatically generated from an OpenAPI specification which has itself been generated by crawling Harvest's API html documentation pages. Hence, some API options might be