Add reference to LIA-3 (ISO/IEC 10967, Part 3)

Author: skirpichev

peps/pep-0812.rst

@@ -634,6 +634,7 @@ Footnotes
 .. [3] ISO/IEC 9899:1999, Annex G.  See `N1256 (final draft)
    <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf>`_.
    https://open-std.org/, WG14. 2007.
+   See also `ISO/IEC 10967: Part 3 <https://en.wikipedia.org/wiki/ISO/IEC_10967>`_.
 
 .. [4] See `Rationale for C99
    <https://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf>`_.