Update README.md to reflect recent changes.

README.md

@@ -1,2 +1,42 @@
 # dredge
-Docker Registry UI
+
+Dredge is a command line tool for working with the Docker Registry V2 API.
+
+## Configuration
+
+Dredge is configured using a simple TOML based configuration file format.
+By default, it will look in the default configuration location for your
+operating system i.e. on Linux this is `~/.config/dredge/dredge.toml`.
+
+You may also override the configuration file at the command line with the
+`-c` or `--config` argument.  The supplied argument must refer to an
+existing file.
+
+The format of the configuration file is simple, and contains only the
+base URL for the registry server.
+
+```toml
+registry_url = "https://localhost:5000"
+```
+
+If Dredge is run without a configuration file present, one will be created
+with the default configuration shown above.
+
+## Usage
+
+### Checking the API Version
+
+Performs a simple API version check.
+
+```sh
+dredge check
+```
+
+### Fetch Repository List
+
+Fetch a sorted list of available repository names from the Registry's
+catalog.
+
+```sh
+dredge catalog
+```