`brew sh`: a shell with superenv loaded
`brew sh`: a shell with superenv loaded

If you need to build software on OS X by hand, a brew shell is the way to do it.

Closes Homebrew/homebrew#14381.

muellermartin/dist,maxim-belkin/brew,amar-laksh/brew_sudo,gordonmcshane/homebrew,MikeMcQuaid/brew,muellermartin/dist,Linuxbrew/brew,aw1621107/brew,MikeMcQuaid/brew,pseudocody/brew,konqui/brew,Homebrew/brew,konqui/brew,gordonmcshane/homebrew,mistydemeo/homebrew,bfontaine/brew,mistydemeo/homebrew,mahori/brew,jmsundar/brew,palxex/brew,reitermarkus/brew,zmwangx/brew,tonyg/homebrew,sjackman/homebrew,JCount/brew,tonyg/homebrew,EricFromCanada/brew,Homebrew/brew,claui/brew,EricFromCanada/brew,ilovezfs/brew,toonetown/homebrew,tonyg/homebrew,mgrimes/brew,rwhogg/brew,DomT4/brew,aw1621107/brew,bfontaine/brew,nandub/brew,hanxue/linuxbrew,MikeMcQuaid/brew,vitorgalvao/brew,MikeMcQuaid/brew,AnastasiaSulyagina/brew,palxex/brew,EricFromCanada/brew,nandub/brew,gregory-nisbet/brew,AnastasiaSulyagina/brew,Homebrew/brew,alyssais/brew,staticfloat/brew,claui/brew,mahori/brew,hanxue/linuxbrew,Linuxbrew/brew,claui/brew,DomT4/brew,alyssais/brew,rwhogg/brew,jmsundar/brew,gregory-nisbet/brew,JCount/brew,AnastasiaSulyagina/brew,JCount/brew,Linuxbrew/brew,mahori/brew,reitermarkus/brew,toonetown/homebrew,maxim-belkin/brew,vitorgalvao/brew,DomT4/brew,mgrimes/brew,muellermartin/dist,Linuxbrew/brew,sjackman/homebrew,gordonmcshane/homebrew,DomT4/brew,Homebrew/brew,zmwangx/brew,amar-laksh/brew_sudo,maxim-belkin/brew,toonetown/homebrew,gregory-nisbet/brew,nandub/brew,vitorgalvao/brew,alyssais/brew,bfontaine/brew,reelsense/brew,zmwangx/brew,mgrimes/brew,JCount/brew,nandub/brew,ilovezfs/brew,sjackman/homebrew,staticfloat/brew,konqui/brew,EricFromCanada/brew,rwhogg/brew,sjackman/homebrew,ilovezfs/brew,amar-laksh/brew_sudo,pseudocody/brew,konqui/brew,mahori/brew,reelsense/brew,pseudocody/brew,claui/brew,hanxue/linuxbrew,aw1621107/brew,reitermarkus/brew,palxex/brew,vitorgalvao/brew,reitermarkus/brew,staticfloat/brew,mistydemeo/homebrew,reelsense/brew,jmsundar/brew