docs: mention riscv64 support in news file

Author: dvarrazzo

NEWS

@@ -7,6 +7,7 @@ What's new in psycopg 2.9.11
 - Add support for Python 3.14.
 - Avoid a segfault passing more arguments than placeholders if Python is built
   with assertions enabled (:ticket:`#1791`).
+- Add riscv64 platform binary packages (:ticket:`#1813`).
 - `~psycopg2.errorcodes` map and `~psycopg2.errors` classes updated to
   PostgreSQL 18.
 - Drop support for Python 3.8.