Add some usage notes

yay for functional readmes?

README.md

@@ -1,3 +1,10 @@
 # image-saver
 
 Ruby app for saving pictures from the web, and annotating them with image-annotate
+
+## Get started
+
+1. Install the dependencies via bundler with `bundle install`
+2. generate the bookmarklet code with `rake bookmarklet` (requires the uglifyjs npm module) and install it in the browser
+3. To test, start the server with `ruby image_app.rb -s`
+4. Go navigate to a page with an image, and save it!