add notable past events to the archive changelog

We want to add to the archive changelog a list of notable changes in archival. This is potentially endless, but here are some big ones that should be there:

• when we started crawling (before project announcement)
• when we started ingesting major forges/instances; ideally we should have an entry for each logo added to our archive coverage list
  • bitbucket git repos (T592)
  • cran (T1709)
  • debian (announcement)
  • github
  • gitlab instances (T1139)
    • gitlab.com (T1111)
    • Inria (T1243)
  • gitorious (T312)
  • google code (T673, swh-loader-svn#617 (closed), swh-loader-mercurial#682 (closed))
  • GNU releases
    • one-off (swh-loader-core#90 (closed))
    • periodic (T1722)
  • HAL (announcement)
  • IPOL (announcement)
  • npm (T1378)
  • NixOS (swh-loader-core#1991 (closed), first lister swh-lister!105 (closed)...) (announcement)
  • Guix (T1352)
  • PyPI (announcement)
  • save code now (announcement)
• major/notable events that have impacted archive coverage or structure
  • what happened on 2020-03-01, explaining why archive started growing much faster (related to github listing/loading)

---

Migrated from T2793 (view on Phabricator)