edit sample app intro

Author: lindseymoore

source/includes/usage-examples/sample-app-intro.rst

@@ -4,7 +4,9 @@ Sample Application
 You can use the following sample application to test the code examples on this
 page. To use the sample application, perform the following steps:
 
-1. Ensure you have the {+php-library+} installed in your project.
+1. Ensure you have the {+php-library+} installed in your project. To learn more 
+   about installing the {+php-library+}, see the 
+   :ref:`Download and Install <php-download-and-install>` guide.
 #. Copy the following code and paste it into a new ``.php`` file.
 #. Copy a code example from this page and paste it on the specified
    lines in the file.