Clarify behavior of `brew search` without an argument
Clarify behavior of `brew search` without an argument

As documented in the man page, when given no arguments, `brew search`
will list all formulae. This is different than giving an *empty*
argument.

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