README: add release notes for 0.2.1
README: add release notes for 0.2.1

zerovm/zerovm-cli,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm,zerovm/zpm