Fix UI strings in Config help for "environment.append-paths"

Summary: Fixes T8939. The parameters on this pht() just got juggled around at some point.

Test Plan: {F654408}

Reviewers: btrahan, avivey, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T8939

Differential Revision: https://secure.phabricator.com/D13694