added how-to on code-signing. code signing certificate is not in git
added how-to on code-signing.
code signing certificate is not in git

HashEngineering/digitalcoin-multibit,monapu/multimona,GroestlCoin/MultiGroestl,myronkaradimas/multibit,bubuntux/multibit,jim618/multibit,HashEngineering/digitalcoin-multibit,langerhans/multidoge,monapu/multimona,bitcartel/multibit,ai-coin/multibit,travisfw/multibit,bitcartel/multibit,bubuntux/multibit,GroestlCoin/MultiGroestl,ai-coin/multibit,myronkaradimas/multibit,travisfw/multibit,langerhans/multidoge,bitcoin-solutions/multibit