Update configuration instructions for Apache 2.4

Summary:
Fixes T4061. Following the instructions in the documentation with Apache 2.4 (which is installed
with Ubuntu 13.10 and other distributions) will result in a "403 forbidden" error.

The instruction provides information on how to fix it.

Test Plan: Tested on apache 2.4 install

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran, asherkin

Maniphest Tasks: T4061

Differential Revision: https://secure.phabricator.com/D7529

src/docs/user/configuration/configuration_guide.diviner

@@ -55,13 +55,24 @@ this:
   </VirtualHost>
 
 If Apache isn't currently configured to serve documents out of the directory
-where you put Phabricator, you may also need to add a section like this:
+where you put Phabricator, you may also need to add `<Directory />` section. The
+syntax for this section depends on which version of Apache you're running.
+(If you don't know, you can usually figure this out by running `httpd -v`.)
+For Apache versions older than 2.4, use this:
 
+  name="Apache Older Than 2.4"
   <Directory "/path/to/phabricator/webroot">
     Order allow,deny
     Allow from all
   </Directory>
 
+For Apache versions 2.4 and newer, use this:
+
+  name="Apache 2.4 and Newer"
+  <Directory "/path/to/phabricator/webroot">
+    Require all granted
+  </Directory>
+
 After making your edits, restart Apache, then continue to "Setup" below.
 
 = Webserver: Configuring nginx =