Document meaning of order of --package-db flags, fixes #12485.
Document meaning of order of --package-db flags, fixes #12485.

Test Plan: none

Reviewers: austin, niteria, bgamari

Reviewed By: niteria

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2514

GHC Trac Issues: #12485

mettekou/ghc,ezyang/ghc,snoyberg/ghc,ezyang/ghc,shlevy/ghc,snoyberg/ghc,sdiehl/ghc,sdiehl/ghc,olsner/ghc,mettekou/ghc,shlevy/ghc,mettekou/ghc,snoyberg/ghc,ezyang/ghc,sdiehl/ghc,olsner/ghc,mettekou/ghc,snoyberg/ghc,sdiehl/ghc,olsner/ghc,shlevy/ghc,olsner/ghc,shlevy/ghc,sdiehl/ghc,snoyberg/ghc,ezyang/ghc,snoyberg/ghc,olsner/ghc,sdiehl/ghc,ezyang/ghc,olsner/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,mettekou/ghc,olsner/ghc,mettekou/ghc,snoyberg/ghc,mettekou/ghc