crosslink reusable library doc

Author: dbu

httplug/tutorial.rst

@@ -78,7 +78,7 @@ still provide a way to interact with this object for your users::
 
         throw $e;
     })->then(function (ResponseInterface $response) {
-        echo 'Response stil available';
+        echo 'Response still available';
 
         return $response;
     }, function (Exception $e) {
@@ -159,4 +159,4 @@ TODO: explain how to handle exceptions, distinction between network exception an
 Writing a reusable package
 --------------------------
 
-TODO: explain the virtual package
+See :ref:`httplug-building-reusable-library`

httplug/virtual-package.rst

@@ -46,6 +46,8 @@ dependency on ``php-http/httplug`` in your ``composer.json`` file.
 However, if your code depends on a minimal version of HTTPlug,
 specify it to have composer report problems rather than the application failing at some point.
 
+.. _httplug-building-reusable-library:
+
 Building a Reusable Library
 ---------------------------