Merge branch 'pb/doc-external-diff-env'

Doc update. * pb/doc-external-diff-env: git.txt: correct stale 'GIT_EXTERNAL_DIFF' description

Junio C Hamano committed Sep 3, 2020 at 12:37 UTC cd332b2a319f00db18b91201cc9a6fafc6adf649

No changes.