Add known issues
Add known issues

1. Limits of Premium Storage blob snapshots
2. Version mismatch between CPI and Stemcell

cloudfoundry-incubator/bosh-azure-cpi-release,gossion/bosh-azure-cpi-release,gossion/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release,AbelHu/bosh-azure-cpi-release,cloudfoundry-incubator/bosh-azure-cpi-release,cloudfoundry-incubator/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release,bingosummer/bosh-azure-cpi-release,AbelHu/bosh-azure-cpi-release,AbelHu/bosh-azure-cpi-release,gossion/bosh-azure-cpi-release