docs: move up paragraph and note

Author: kenjis

user_guide_src/source/installation/index.rst

@@ -11,6 +11,15 @@ Which is right for you?
 - If you would like the simple "download & go" install that CodeIgniter3
   is known for, choose the manual installation.
 
+However you choose to install and run CodeIgniter4, the
+`user guide <https://codeigniter4.github.io/userguide/>`_ is accessible online.
+
+.. note:: Before using CodeIgniter 4, make sure that your server meets the
+    :doc:`requirements </intro/requirements>`, in particular the PHP
+    version and the PHP extensions that are needed.
+    You may find that you have to uncomment the ``php.ini`` "extension"
+    lines to enable "curl" and "intl", for instance.
+
 .. toctree::
     :titlesonly:
 
@@ -21,12 +30,3 @@ Which is right for you?
     upgrading
     troubleshooting
     repositories
-
-However you choose to install and run CodeIgniter4, the
-`user guide <https://codeigniter4.github.io/userguide/>`_ is accessible online.
-
-.. note:: Before using CodeIgniter 4, make sure that your server meets the
-    :doc:`requirements </intro/requirements>`, in particular the PHP
-    version and the PHP extensions that are needed.
-    You may find that you have to uncomment the ``php.ini`` "extension"
-    lines to enable "curl" and "intl", for instance.