Update README.md with more usage examples

README.md

@@ -30,13 +30,29 @@ url     = 'https://status.rubygems.org'
 request = {'Version' => 'HTTP/1.1'}
 cached  = {}
 
+# test without cached response
 CacheRules.validate url, request, cached
 
-=>  {:body=>nil, :code=>307, :headers=>{"Cache-Lookup"=>"MISS", "Location"=>"https://status.rubygems.org"}}
+=> {:body=>nil, :code=>307, :headers=>{"Cache-Lookup"=>"MISS", "Location"=>"https://status.rubygems.org"}}
+
+cached  = { "Date" => {"timestamp"=>1420095825}, "X-Cache-Req-Date"  => {"timestamp"=>1420268625}, "X-Cache-Res-Date"  => {"timestamp"=>1420268625} }
+
+# test with cached response (status code 200 because no ETag or If-None-Match supplied)
+CacheRules.validate url, request, cached
+
+=> {:body=>"stale", :code=>200, :headers=>{"Date"=>"Wed, 21 Feb 2018 05:09:27 GMT", "Age"=>"99094242", "Warning"=>"110 - \"Response is Stale\"", "Cache-Lookup"=>"STALE"}}
+
+request = {"Version"=>"HTTP/1.1", "If-None-Match"=>"*"}
+cached  = { "Date" => {"timestamp"=>1519190160}, "X-Cache-Req-Date"  => {"timestamp"=>1519190160}, "X-Cache-Res-Date"  => {"timestamp"=>1519190160} }
+
+# test with cached response (status code 304 because If-None-Match supplied)
+=> {:body=>nil, :code=>304, :headers=>{"Date"=>"Wed, 21 Feb 2018 05:15:01 GMT", "Age"=>"241", "Warning"=>"110 - \"Response is Stale\"", "Cache-Lookup"=>"STALE"}}
 ```
 
 The `request` headers must be a Ruby Hash or Array of 2-element Arrays.
-The `cached` headers must already have been normalized by this caching library.
+The `cached` headers must already have been normalized by this caching library, i.e: they **must** include the `Date['timestamp'], X-Cache-Req-Date['timestamp'], X-Cache-Res-Date['timestamp']` array keys.
+
+See `test/` directory for more examples.
 
 ## Decision tables