Format markdown and improve readme content
Format markdown and improve readme content

Use our standard requirements section with information on the supported platforms and required cookbooks
Fix some spelling errors
Remove reference to issues.md
Add cookbook version badge
Add some syntax highlighting to code blocks
Update copyright

mknapik/jenkins,chef-cookbooks/jenkins,b-dean/jenkins,b-dean/jenkins,autoclone/jenkins-cookbook,mknapik/jenkins,juliandunn/jenkins,gshively11/jenkins,StephenKing/chef-cookbook-jenkins,StephenKing/chef-cookbook-jenkins,Sauraus/jenkins,opscode-cookbooks/jenkins,samdunne/jenkins,opscode-cookbooks/jenkins,autoclone/jenkins-cookbook,Sauraus/jenkins,Sauraus/jenkins,daften/cookbook-jenkins,juliandunn/jenkins,StephenKing/chef-cookbook-jenkins,chef-cookbooks/jenkins,dshvedchenko/jenkins,daften/cookbook-jenkins,gshively11/jenkins,dshvedchenko/jenkins,dshvedchenko/jenkins,Dispader/jenkins,samdunne/jenkins,daften/cookbook-jenkins,gshively11/jenkins,chef-cookbooks/jenkins,b-dean/jenkins,Dispader/jenkins,autoclone/jenkins-cookbook,mknapik/jenkins,Dispader/jenkins,samdunne/jenkins,juliandunn/jenkins,opscode-cookbooks/jenkins