Update link README.md

[taivlam]

• Link to former link https://docs.makedeb.org/mpr/list-of-mpr-helpers/ is now not found in makedeb docs
  • Mist page is currently closest match among makdedeb doc pages
  • However, after looking at the latest snapshot from March 2022, the features explicitly listed are in the first section of Mist's README

[taivlam]

Both PR #20 and #35 are trying to fix the same link; however, the proposed link of https://docs.makedeb.org/using-the-mpr/list-of-mpr-helpers/ now redirects to https://docs.makedeb.org/using-the-mpr/mist-the-mpr-cli/.

Still, linking to Mist's GH repo seems to currently be currently more resistant to link rot than the makedeb docs.