Changelogs are stored in src/changelog directory.
log4j-changelog is used to generate AsciiDoc-formatted release notes during Maven pre-site phase and export them to target/generated-sources/site/asciidoc/changelog directory.
These exported AsciiDoc files are not committed, since they are only relevant for the website, and they cause merge-conflicts between feature branches.
./mvnw site command can be used to manually generate these files.
See log4j-changelog project for further details; how to use this changelog system, what steps are needed while making a new release, etc.
For the impatient, simply copy one of the existing <issueId>_<summary>.xml files in src/changelog/.2.x.x directory and adapt to your needs.
See the official documentation for details.