yardopts: specify "extra" files.
yardopts: specify "extra" files.

The current .yardopts is treating extra .md files as source code rather
than registering them as "extra files". YARD needs a "-" to separate
source from non-source files.

Closes Homebrew/homebrew#33362.

Signed-off-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

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