Advise the use of absolute paths, fixes #4259

doc/01-basic-usage.md

@@ -152,7 +152,7 @@ For libraries that specify autoload information, Composer generates a
 autoloading for free.
 
 ```php
-require 'vendor/autoload.php';
+require __DIR__ . '/vendor/autoload.php';
 ```
 
 This makes it really easy to use third party code. For example: If your project
@@ -192,7 +192,7 @@ the return value of the include call in a variable and add more namespaces.
 This can be useful for autoloading classes in a test suite, for example.
 
 ```php
-$loader = require 'vendor/autoload.php';
+$loader = require __DIR__ . '/vendor/autoload.php';
 $loader->add('Acme\\Test\\', __DIR__);
 ```