Document changed configure option

Cf. <php/php-src#3632>.

git-svn-id: http://svn.php.net/repository/phpdoc/en@345963 c90b9560-bf6c-de11-be94-00142212c4b1

Author: cmb

trunk/reference/image/configure.xml

@@ -96,6 +96,8 @@
       <entry>
        To enable support for FreeType 2 add
        <option role="configure">--with-freetype-dir=DIR</option>.
+       As of PHP 7.4.0 use <option role="configure">--enable-freetype</option>
+       instead, which relies on <productname>pkg-config</productname>.
       </entry>
      </row>
      <row>