We have a lot of quality-of-life features, more art, bug fixes, and perf improvements all coming in v1.1 - which we hope to release in the next week or two. We haven't updated the docs yet but in v1.1 you will be able to right click to quickly swap between "add" and "remove" modes when editing Layers. We are also improving the Item adding/editing experience a LOT.
If you haven't checked out the TerraScriber documentation, we are keeping that updated with screenshots, tips, and more. Thanks again for using TerraScriber!