Stop registering the PDF extension in the plugin routes configuration.

By default, using plugin routes to register extensions for application
routes happens too late, which will cause the automatic PDF view
functionality to not be triggered for URLs with the `pdf` extension.
Therefore the extension is best to be registered manually when needed.

Resolves FriendsOfCake#147

README.md

@@ -50,9 +50,28 @@ composer require mpdf/mpdf
 
 In `config/bootstrap.php` add:
 ```php
-Plugin::load('CakePdf', ['bootstrap' => true, 'routes' => true]);
+Plugin::load('CakePdf', ['bootstrap' => true]);
 ```
 
+If you plan to use [the PDF view functionality](#1-render-as-pdf-including-forced-download-in-the-browser-with-pdfview)
+that automatically renders and returns the PDF for sending it to the browser, you should also register the `pdf`
+extension in your `config/routes.php` file, either globally before the routes that should be affected:
+
+```php
+Router::extensions(['pdf']);
+```
+
+or for a specific route scope:
+
+```php
+Router::scope('/', function (\Cake\Routing\RouteBuilder $routes) {
+    $routes->extensions(['pdf']);
+    // ...
+});
+```
+
+Further setup information can be found in the usage section.
+
 
 ## Configuration
 
@@ -144,11 +163,15 @@ You can create PDF view and layout files for your controller actions and have th
 Place the view templates in a 'pdf' subdir, for instance `src/Template/Invoices/pdf/view.ctp`
 Layouts will be in `src/Template/Layouts/pdf/default.ctp`
 
-Make sure your InvoicesController has RequestHandler Component in the `$components` array.
-Browse to http://localhost/invoices/view/1.pdf
+Make sure your `InvoicesController` class
+[loads the `RequestHandler` component](http://book.cakephp.org/3.0/en/controllers/components/request-handling.html)
+and browse to `http://localhost/invoices/view/1.pdf`
 
 Additionally you can map resources by adding `Router::mapResources(['Invoices']);` to your routes
-file and you can access the same document at http://localhost/invoices/1.pdf
+file and you can access the same document at `http://localhost/invoices/1.pdf`
+
+In case you don't want to use the `pdf` extension in your URLs, you can omit registering it in your routes
+configuration, and have your requests send a `Accept: application/pdf` header instead.
 
 
 ### 2: Create PDF for email attachment, file storage etc.