Add RHEL upgrade tooling

[bocekm]

Please add:

• The Preupgrade Assistant
  • Repo: https://github.com/upgrades-migrations/preupgrade-assistant/
  • Website: Null
  • Description: Assists with in-place upgrading RHEL 6 to RHEL 7
• The Red Hat Upgrade Tool
  • Repo: https://github.com/upgrades-migrations/redhat-upgrade-tool/
  • Website: Null
  • Description: In-place upgrades RHEL 6 to RHEL 7
• Leapp:
  • Repo: https://github.com/leapp-to/
  • Website: https://leapp-to.github.io
  • Description: In-place upgrades RHEL 7 to future versions of RHEL

I'm not sure about the category but I would pick Platform.