Add usage example to README.md

README.md

@@ -5,7 +5,27 @@
 > _This is still in early stages of development, so proceed with caution when using this in a production application.
 > Any bug reports, feature requests, or general feedback at this point would be greatly appreciated._
 
-SZNAltmetric is a [Altmetric API](http://api.altmetric.com) client for iOS and Mac OS X. It’s built on top of [AFNetworking](http://www.github.com/AFNetworking/AFNetworking) to deal with network operations.
+SZNAltmetric is an [Altmetric API](http://api.altmetric.com) client for iOS and Mac OS X. It’s built on top of [AFNetworking](http://www.github.com/AFNetworking/AFNetworking) to deal with network operations.
+
+## Example Usage
+
+We wanted to make it as simple as possible to fetch details about an article from the API, so here is how it looks like:
+
+```objectivec
+// Let’s specify an API key (optional)
+SZNAltmetricAPIClient *client = [SZNAltmetricAPIClient sharedClient];
+client.APIKey = @"###abc123###";
+
+// Okay, now let’s fetch some data
+[client fetchArticleWithDOI:@"###DOI###"
+                    success:^(SZNAltmetricArticle *article) {
+                        // We have the article, 
+                        // we can log the Altmetric score
+                        NSLog(@"%@", [article.score stringValue]);
+                    } failure:nil];
+```
+
+As you can see, we have just requested an article based on its DOI (you can also use Altmetric ID, PubMed ID, arXiv ID, and ADS Bibcode). What you get is a `SZNAltmetricArticle` object, containing all the identifiers, the Altmetric score, and even the URLs to the “donuts” images.
 
 ## Credits