Add unreleased section to CHANGELOG (#332)
Add unreleased section to CHANGELOG (#332)

Document unreleased features in the CHANGELOG.

Signed-off-by: Ben Kochie <9bbf917dc63fbaa40c67921332d26cf16a50db75@gmail.com>
roman-vynar/mysqld_exporter,prometheus/mysqld_exporter,prometheus/mysqld_exporter,roman-vynar/mysqld_exporter