Update README

README.md

@@ -1,7 +1,17 @@
-Goal:
+# `dlt` - Docker Layer Tool
 
-- Specify a base image name
+Helpers for performing advanced manipulations of Docker image layers.
-- Specify a final image name
+
-- Identify the last layer of the base image
+## `isolate [from image] [to image] [--output=path] [--as=image name] [--no-base]`
-- Export the intermediate layers that the final image adds to the base image
+
-- Reimport those as a single layer
+Given an image `[to image]` that is based on `[from image]`, extract (or... isolate) the files that changed ONLY since the `[from image]` and output it as a `.tar` file.
+
+Optionally, using the `--as` flag, create a new image based on `[from image]` that has a single additional layer with all the filesystem changes.
+
+This command may be useful if you want to flatten an image but still make use of upstream caching of your base image layers. If the `--no-base` flag is specified, the resulting image will contain _only_ the changed files, excluding the base image.
+
+Example:
+
+```shell
+./dlt.bash isolate ubuntu:22.04 user/myapp:latest --output=changes.tar --as user/myapp:flattened
+```