async function regenerateChangelog(packageName) {
  const path = changelogPath(packageName)
  const separator = `<a name="before-release-process"></a>`
  const contents = String(fs.readFileSync(path))
  const parts = contents.split(separator)

  if (parts.length !== 2) {
    throw new Error(`Could not find demarcation ${separator.trim()} in ${path}`)
  }
  const changeLog = await generateChangelog(packageName)

  const updatedChangelogParts = [
    renderHeader(packageName),
    `\n\n`,
    changeLog,
    `\n\n`,
    separator,
    parts[1],
  ]

  fs.writeFileSync(path, updatedChangelogParts.join(``))
  console.log(`Updated ${path}`)
}
Completely regenerate the top part of the changelog with veresions published via the new release process.

Relies on presence of `<a name="before-release-process"></a>\n` separator in the CHANGELOG.md
document as a demarcation of parts of the document before/after the release process was introduced.