[libxml2] add documentaiton for xmllint exit code 10

[Nick Wellnhofer <nwellnhof src gnome org>]

commit bdd482c2ec88997f74302dd384bdd1c97a1a5718
Author: Rainer M. Canavan <rainer canavan avenga com>
Date:   Mon Jul 5 18:48:10 2021 +0200

    add documentaiton for xmllint exit code 10
    
    Closes: https://gitlab.gnome.org/GNOME/libxml2/-/issues/280

 doc/xmllint.xml | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/doc/xmllint.xml b/doc/xmllint.xml
index 1008179b..f272287e 100644
--- a/doc/xmllint.xml
+++ b/doc/xmllint.xml
@@ -899,6 +899,13 @@
        </listitem>
                </varlistentry>
 
+               <varlistentry>
+       <term><errorcode>10</errorcode></term>
+       <listitem>
+               <para>XPath evaluation error</para>
+       </listitem>
+               </varlistentry>
+
        </variablelist>
 </refsect1>