add key_proxy to readme
add key_proxy to readme

PolicyStat/apt,daptiv/apt,patcon/apt,trinitronx/apt,protec-cookbooks/apt,protec-cookbooks/apt,MarkRoddy/apt,Altiscale/apt,PolicyStat/apt,VertiPub/apt,chrisroberts/apt,h4ck3rm1k3/apt,chef-cookbooks/apt,Altiscale/apt,aerickson/apt,balmbees/apt,swistaczek/apt,BarthV/apt,Banno/apt,scalarae/apt,ouranos/apt,Alukardd/cookbook-apt,scalarae/apt,andrewgross/apt,Shopify/chef-apt,Tealium/apt,h4ck3rm1k3/apt,adambrett-forks/chef-apt,BarthV/apt,NREL-cookbooks/apt,samstokes/apt,puckel/apt,Rockstar04/apt,mchesnut/apt,ikkyotech/OpsworksNodeAddons,puckel/apt,chef-cookbooks/apt,brumschlag/apt,ortoo/apt,VertiPub/apt,MattMencel/apt,brumschlag/apt,portertech/apt,sabcio/apt,yola/apt-cookbook,rackspace-cookbooks/rackspace_apt,edmunds-chef/apt,opscode-cookbooks/apt,Alukardd/cookbook-apt,tmatilai/chef-apt,eteeselink/apt,ikkyotech/OpsworksNodeAddons,tomgl/apt,Rockstar04/apt,mattray/apt,opscode-cookbooks/apt,whiteley/apt,edmunds-chef/apt,balmbees/apt,patcon/apt,wrbooth/apt,pwnieexpress/apt,Tealium/apt,CodePen/apt,democracyworks/apt,pwnieexpress/apt,gswallow/apt