Release script tweaks
Release script tweaks

- be more helpful if update_changelog is not installed
- behave sanely if v is omitted on tag arg

williamboman/matrix-js-sdk,williamboman/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,williamboman/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk