update documentation

doc/user/stored-procedures.xml

@@ -891,6 +891,24 @@ lua box.dostring('local f = function(key) t=box.select(0, 0, key); if t ~= nil t
             </programlisting>
         </listitem>
     </varlistentry>
+    <varlistentry>
+        <term>
+            <emphasis role="lua">box.raise(errcode, errtext)</emphasis>
+        </term>
+        <listitem>
+            <para>
+                Throws client error. Lua procedure can emulate any
+                request errors (for example: unique key exception).
+            </para>
+            <bridgehead renderas="sect4">Example</bridgehead>
+            <programlisting>
+                lua box.raise(123, 'test')
+                ---
+                error: 'test'
+                ...
+            </programlisting>
+        </listitem>
+    </varlistentry>
     <varlistentry>
         <term>
             <emphasis role="lua">box.auto_increment(space_no, ...)</emphasis>