Created HTTP Caching (markdown)

HTTP-Caching.md

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+Flight provides built-in support for HTTP level caching. If the caching condition is met,
+Flight will return an HTTP `304 Not Modified` response. The next time the client requests the same resource,
+they will be prompted to use their locally cached version.
+
+## Last-Modified
+
+You can use the `lastModified` method and pass in a UNIX timestamp to set the date and time a page was last modified.
+The client will continue to use their cache until the last modified value is changed.
+
+    Flight::route('/news', function(){
+        Flight::lastModified(1234567890);
+        echo 'This content will be cached.';
+    });
+
+## ETag
+
+ETag caching is similar to Last-Modified, except you can specify any id you want for the resource:
+
+    Flight::route('/news', function(){
+        Flight::etag('my-unique-id');
+        echo 'This content will be cached.';
+    });
+
+Keep in mind that calling either `lastModified` or `etag` will both set and check the cache value.
+If the cache value is the same between requests, Flight will immediately send an HTTP 304 response and stop
+processing.