Installation refine (REDO) (PR #2612)

discourse
#1

As @SamSaffron suggested in #2398, I redo that PR.

Ref: https://github.com/discourse/discourse/pull/2398#issuecomment-50428250

GitHub

#2

You’ve signed the CLA, lazywei. Thank you! This pull request is ready for review.

#3

Thanks!

#4
#5