Update 'Usage'

Usage.md

@@ -2,6 +2,32 @@
 
 Using Fresh is as simple as falling off a log. Just run it while in a directory that contains a `docker-compose.yml` file, and Fresh will go and check for updates to any registries you have authenticated against. This means it currently can't be used to check images from dockerhub, but it works great for private registries.
 
+### Limiting updates
+
+When using docker-compose, Fresh will call on `docker-compose pull` and `docker-compose up` without any parameters causing all updated images to be fetched. This may not be desired however, in which case you can get more control over what is updated by using the `--updated` or `--only` flags.
+
+```shell
+# Update everything
+$ fresh.phar
+
+# Only update the images alpha and beta whenever new images exist for any service
+$ fresh.phar --only alpha,beta
+
+# Only update the services that have updated
+$ fresh.phar --updated
+```
+
+### Checking only
+
+To just check for updates, use the `--check` option. The exitcode will be set if there are new images available, and you can do your own magic. This can be combined with `--image` to check a specific image:
+
+```shell
+# Call on update.sh if new stuff exists
+$ fresh.phar --check || ./update.sh
+```
+
+## Notifications and Hooks
+
 ### Slack/Mattermost Webhooks
 
 Fresh can invoke a Slack-compatible webhook to notify before anything is actually updated. To do this, use the `--slack` flag followed by the webhook URL