Update docs about versioning and images

Author: djfarrelly

README.md

@@ -4,6 +4,14 @@ A straightforward static asset uploader which versions files by their contents
 and generates a json file for your application to read the uploaded file
 locations from.
 
+## Versioned files and Images
+
+`.js` and `.css` files are versioned during upload using a hash of the file's
+contents as to allow for cache-busting.
+
+Images and other files are *not* versioned to allow for maximum caching and due
+to their contents not changing very often like `.css` and `.js` files do.
+
 ## Usage
 
 Ensure your AWS credentials environment variables are set (`AWS_ACCESS_KEY_ID`,
@@ -30,7 +38,7 @@ Usage of buffer-static-upload:
 For example, you can use glob patterns to match multiple sets of files:
 
 ```
-buffer-static-upload -files "public/js/**/*.js,public/css/*.css" -bucket my-bucket
+buffer-static-upload -files "public/js/**/*.js,public/css/*.css,public/img/*.*" -bucket my-bucket
 ```
 
 This will generate a `staticAssets.json` file in this directory like this:
@@ -39,7 +47,8 @@ This will generate a `staticAssets.json` file in this directory like this:
 {
   "public/css/style.css": "https://my-bucket.s3.amazonaws.com/public/css/style.11985b07e3121564a73d4d6821bfcfe7.css",
   "public/js/x/another.js": "https://my-bucket.s3.amazonaws.com/public/js/x/another.bfa2d0f60841707efe7be0a94c4caacf.js",
-  "public/js/script.js": "https://my-bucket.s3.amazonaws.com/public/js/script.d55002b60fcfff0b3d355184d23af6f7.js"
+  "public/js/script.js": "https://my-bucket.s3.amazonaws.com/public/js/script.d55002b60fcfff0b3d355184d23af6f7.js",
+  "public/img/home.jpg": "https://my-bucket.s3.amazonaws.com/public/img/home.jpg",
 }
 ```