Readme is incomplete, help is incomplete

[kikito]

On this makefile we can see several options that the generator admits but they are not documented, neither in this repo's readme nor when running changelog --help:

https://github.com/Kong/kong/blob/master/changelog/Makefile#L52-L71

        changelog --debug=$(DEBUG) generate \
            --repo-path . \
            --changelog-paths $(VERSION)/kong,$(UNRELEASED_DIR)/kong \
            --title Kong \
            --github-issue-repo $(OWNER_REPO) \
            --github-api-repo $(OWNER_REPO) \
            --with-jiras \
            >> $(VERSION).md; \
    fi
    @if [ -n "$$(shopt -s nullglob; echo $(UNRELEASED_DIR)/kong-manager/*.yml)" ] || \
        [ -n "$$(shopt -s nullglob; echo $(VERSION)/kong-manager/*.yml)" ] ; then \
        changelog --debug=$(DEBUG) generate \
            --repo-path . \
            --changelog-paths $(VERSION)/kong-manager,$(UNRELEASED_DIR)/kong-manager \
            --title Kong-Manager \
            --github-issue-repo Kong/kong-manager \
            --github-api-repo $(OWNER_REPO) \
            --with-jiras \
            >> $(VERSION).md; \

[vm-001]

@kikito Try changelog generate -h

changelog generate -h
NAME:
   changelog generate

USAGE:
   changelog generate [command options] [arguments...]

DESCRIPTION:
   The generate command output the generated changelog markdown to /dev/stdout

OPTIONS:
   --repo-path value                                    The repository path (/path/to/your/repository)
   --changelog-path value                               The changelog folder relative path (changelog/unreleased/kong)
   --title value                                        The title name (Kong)
   --changelog-paths value [ --changelog-paths value ]  The changelog folder relative paths (changelog/unreleased/kong)
   --github-issue-repo value                            The repo name that is used to compose the GitHub issue link. (OWNER/REPO)
   --github-api-repo value                              The repo name that is used to compose the GitHub URL to retrieve data. (OWNER/REPO)
   --with-jiras                                         Display Jira links (default: false)
   --help, -h                                           show help