update link to new mysqlclient module and recommend update in upgrading.txt

Author: cmeerw

doc/installation.txt

@@ -1115,7 +1115,7 @@ from installation and scripts.
 .. _apache: http://httpd.apache.org/
 .. _flup: https://pypi.org/project/flup/
 .. _mod_python: http://www.modpython.org/
-.. _MySQLdb: http://sourceforge.net/projects/mysql-python
+.. _MySQLdb: https://pypi.org/project/mysqlclient/
 .. _Psycopg: http://initd.org/software/initd/psycopg
 .. _pysqlite: http://pysqlite.org/
 .. _`adding MySQL users`:

doc/mysql.txt

@@ -16,7 +16,7 @@ to install:
    if you have no other choice). If you're running < 4.0.18 (but not <4.0)
    then you'll need to use BDB to pass all unit tests. Edit the
    ``roundup/backends/back_mysql.py`` file to enable DBD instead of InnoDB.
-2. Python MySQL interface - http://sourceforge.net/projects/mysql-python
+2. Python MySQL interface - https://pypi.org/project/mysqlclient/
 
 
 Other Configuration

doc/upgrading.txt

@@ -30,6 +30,14 @@ Roundup now uses the ``gpg`` module instead of ``pyme`` to process PGP
 mail.  If you have PGP processing enabled, make sure the ``gpg``
 module is installed.
 
+MySQL client module
+-------------------
+
+Although the ``MySQLdb`` module from
+https://pypi.org/project/MySQL-python/ is still supported, it is
+recommended to switch to the updated module from
+https://pypi.org/project/mysqlclient/.
+
 Migrating from 1.5.1 to 1.6.0
 =============================