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

vikraman/ghc,shlevy/ghc,vTurbine/ghc,sdiehl/ghc,snoyberg/ghc,vikraman/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,vTurbine/ghc,sdiehl/ghc,vTurbine/ghc,olsner/ghc,snoyberg/ghc,vikraman/ghc,ezyang/ghc,olsner/ghc,mcschroeder/ghc,snoyberg/ghc,shlevy/ghc,ezyang/ghc,nushio3/ghc,mcschroeder/ghc,shlevy/ghc,sgillespie/ghc,oldmanmike/ghc,mcschroeder/ghc,nushio3/ghc,sdiehl/ghc,tjakway/ghcjvm,sdiehl/ghc,sgillespie/ghc,oldmanmike/ghc,nushio3/ghc,vikraman/ghc,ezyang/ghc,tjakway/ghcjvm,oldmanmike/ghc,ezyang/ghc,vikraman/ghc,nushio3/ghc,vTurbine/ghc,olsner/ghc,mettekou/ghc,mettekou/ghc,sgillespie/ghc,tjakway/ghcjvm,oldmanmike/ghc,nushio3/ghc,sdiehl/ghc,oldmanmike/ghc,nushio3/ghc,vikraman/ghc,mettekou/ghc,snoyberg/ghc,tjakway/ghcjvm,vTurbine/ghc,olsner/ghc,olsner/ghc,mettekou/ghc,snoyberg/ghc,mcschroeder/ghc,tjakway/ghcjvm,tjakway/ghcjvm,vikraman/ghc,sgillespie/ghc,shlevy/ghc,nushio3/ghc,ezyang/ghc,oldmanmike/ghc,mcschroeder/ghc,sgillespie/ghc,shlevy/ghc,snoyberg/ghc,shlevy/ghc,vTurbine/ghc,vTurbine/ghc,mcschroeder/ghc,shlevy/ghc,sgillespie/ghc,mettekou/ghc,snoyberg/ghc,mettekou/ghc,olsner/ghc,olsner/ghc,ezyang/ghc,mettekou/ghc,sgillespie/ghc,mcschroeder/ghc,oldmanmike/ghc,tjakway/ghcjvm