Remove metadata.json and update application readme.
Remove metadata.json and update application readme.

* Metadata.json can be generated with the rake tasks.
* Use 'metadata[cookbook]' and 'metadata_all' to generate .json.
* Application readme needed a few more clarification points.

leoditommaso/postfix,nilroy/postfix,ianneub/postfix,clkao-cookbooks/postfix,ashmere/postfix,flaccid/postfix,i11/postfix,opscode-cookbooks/postfix,mawatech/postfix,tanordheim/opscode-chef-postfix,atomic-penguin/postfix,tas50/postfix,jtimberman/postfix,jusbrasil/postfix-cookbook,ampledata/cookbook-postfix,fabn/postfix,chrisjbray/postfix,gnowxilef/cookbook-postfix,CarnegieLearningWeb/chef-postfix,nbudin/postfix,tejaycar/postfix,gensen/postfix,elliotkendallUCSF/postfix,heat-cookbooks/postfix,paabulaabu/postfix,rafaelmagu/postfix,millisami/milli-chef-postfix,djwhitt/chef-postfix,chef-cookbooks/postfix,zuazo-forks/chef-cookbooks-postfix,L2G/postfix,Agiley/postfix,voroniys/postfix,heat-cookbooks/postfix,opscode-cookbooks/postfix,brint/postfix,Lostmyname/postfix,petere/postfix,Lostmyname/postfix,tezz123/postfix,jusbrasil/postfix-cookbook,VertiPub/postfix,interactive-investor-ltd/postfix,chrisjbray/postfix,oli-g/postfix,kkeane/postfix,Maks3w/postfix,nilroy/postfix,nuoyan/postfix,tigris/postfix,zuazo-forks/chef-cookbooks-postfix,nebulab/postfix,tinderfields/postfix,jdamick/postfix,NREL-cookbooks/postfix,interactive-investor-ltd/postfix,Koded/postfix,higanworks-cookbooks/postfix,tcroiset/postfix,cookbooks/hw-postfix,chrodriguez/postfix,rackspace-cookbooks/rackspace_postfix,claco/postfix,eric-al/postfix,leoditommaso/postfix,chef-cookbooks/postfix,mawatech/postfix,yakara-ltd/postfix,mlyndaker/postfix,cookbooks/oc-postfix,yakara-ltd/postfix,aki77/postfix,harmdewit/postfix,team-lab/lab-chef-postfix,voroniys/postfix,mlyndaker/postfix,gnowxilef/cookbook-postfix,CarnegieLearningWeb/chef-postfix