Resolve #577 Fix URL pointing to how to set up extension directory (!581) · Merge requests · Documentation / Docs / Developer Documentation

Created by: seamuslee001

ping @eileenmcnaughton @MegaphoneJon @jptillman

This points the documentation to the correct place for creating the Extensions directory which is in the Sysadmin guide not developer

Resolve #577 Fix URL pointing to how to set up extension directory