Cleaned up the code signing instructions: - make sure to delet the .cer file on the desktop - added section that describes what to do when you re-install a new OS where    you still have an old code signing certificate around.
Cleaned up the code signing instructions:
- make sure to delet the .cer file on the desktop
- added section that describes what to do when you re-install a new OS where 
  you still have an old code signing certificate around.



git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@167389 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb