Document the resource_usage param for pcntl_waitid (php#3854)

Author: vrza

reference/pcntl/functions/pcntl-waitid.xml

@@ -14,6 +14,7 @@
    <methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>id</parameter><initializer>&null;</initializer></methodparam>
    <methodparam choice="opt"><type>array</type><parameter role="reference">info</parameter><initializer>[]</initializer></methodparam>
    <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer><constant>WEXITED</constant></initializer></methodparam>
+   <methodparam choice="opt"><type>array</type><parameter role="reference">resource_usage</parameter><initializer>[]</initializer></methodparam>
   </methodsynopsis>
   <para>
    Obtains status information pertaining to termination, stop, and/or continue
@@ -245,6 +246,18 @@
      </para>
     </listitem>
    </varlistentry>
+   <varlistentry>
+    <term><parameter>resource_usage</parameter></term>
+    <listitem>
+     <para>
+      The <parameter>resource_usage</parameter> parameter is set to an array
+      containing resource usage statistics from the child process.
+
+      This is supported either if the wait6 system call is available
+      (e.g. on FreeBSD), or on Linux through the raw waitid system call.
+     </para>
+    </listitem>
+   </varlistentry>
   </variablelist>
  </refsect1>