Document max_input_vars impact on parse_str() (fixes #4521)

Author: philip

reference/strings/functions/parse-str.xml

@@ -142,6 +142,15 @@ echo $output['My_Value']; // Something
  <refsect1 role="notes">
   &reftitle.notes;
 
+  <note>
+   <para>
+    <function>parse_str()</function> is affected by the <link linkend="ini.max-input-vars">max_input_vars</link>
+    directive. Exceeding this limit triggers an <constant>E_WARNING</constant>,
+    and any variables beyond the limit are not added to the result array.
+    The default is 1000; adjust <link linkend="ini.max-input-vars">max_input_vars</link> as needed.
+   </para>
+  </note>
+
   <note>
    <para>
     All variables created (or values returned into array if second parameter is set)