Added note about PIE to a few PECL help pages (#4755)

install/pecl.xml

@@ -6,6 +6,7 @@
 
  <sect1 xml:id="install.pecl.intro">
   <title>Introduction to PECL Installations</title>
+  &pecl.moving.to.pie;
   <simpara>
    &link.pecl; is a repository of PHP extensions that are made available via the
    <link xlink:href="&url.php.pear;">PEAR</link>
@@ -46,6 +47,7 @@
 
  <sect1 xml:id="install.pecl.downloads">
   <title>Downloading PECL extensions</title>
+  &pecl.moving.to.pie;
   <simpara>
    There are several options for downloading PECL extensions, such as:
   </simpara>
@@ -119,6 +121,7 @@ $ svn checkout https://svn.php.net/repository/pecl/extname/trunk extname
 
  <sect1 xml:id="install.pecl.windows">
   <title>Installing a PHP extension on Windows</title>
+  &pecl.moving.to.pie;
   <para>
    There are two ways to load a PHP extension on Windows: either compile it into
    PHP, or load the DLL.

language-snippets.ent

@@ -2213,6 +2213,14 @@ for this <acronym xmlns="http://docbook.org/ns/docbook">PECL</acronym> extension
 <!ENTITY pecl.moved-ver 'This extension has been moved to the &link.pecl;
 repository and is no longer bundled with PHP as of PHP '>
 
+<!ENTITY pecl.moving.to.pie '<note xmlns="http://docbook.org/ns/docbook">
+ <simpara>
+  PHP Installer for Extensions (<acronym>PIE</acronym>) is a new tool that will deprecate PECL.
+  We recommend using PIE to install extensions.
+  Find out more at <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://github.com/php/pie">https://github.com/php/pie</link>
+ </simpara>
+</note>'>
+
 <!ENTITY warn.pecl.unmaintained '<warning xmlns="http://docbook.org/ns/docbook">
  <simpara>This extension is <emphasis>unmaintained</emphasis>.</simpara>
 </warning>'>