Keep release notes brief and informative. They do not need to go into detail covering what went into a fix or enhancement; only include enough information to identify what change went into the application, and a brief description.
Do not assume that the reader is technically inclined unless your notes are specifically for a technical audience. Instead focus on the functionality which was changed or is affected. Each note consists of a header and a description. The header will explain what the feature is, and the description conveys enough information to explain what occurred.