Update changelog. Ref #879.

CHANGES.rst

+v30.4.0
+-------
+
+* #879: For declarative config:
+  - read_configuration() now accepts ignore_option_errors argument. This allows scraping tools to read metadata without a need to download entire packages. E.g. we can gather some stats right from GitHub repos just by downloading setup.cfg.
+  - packages find: directive now supports fine tuning from a subsection. The same arguments as for find() are accepted.
+
 v30.3.0
 -------