Better document behavior of -Wmissed-specialisations
Better document behavior of -Wmissed-specialisations

Test Plan: Read it

Reviewers: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1829

(cherry picked from commit 6e2658f67bcdbc7fd0ebd2ef6abcd13a6bec80bc)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc