Update README.md.

Signed-off-by: Benjamin P. Jung <headcr4sh@gmail.com>

README.md

@@ -1,19 +1,22 @@
 # Gravatar API Client for Rust
 
+A small library to access the Gravatar API,
+inspired by [rust-gravatar](https://github.com/chowdhurya/rust-gravatar/).
+
 ## Example Usage
 
 ```rust
+extern crate gravatar_api;
 use gravatar_api::avatars;
 
-fn main() {
-    println!(
-        "{}",
-        avatars::Avatar::builder("john.doe@example.com")
-            .size(512)
-            .default(avatars::Default::RoboHash)
-            .rating(avatars::Rating::G)
-            .build()
-            .image_url()
-    );
-}
-``
+let url = avatars::Avatar::builder("john.doe@example.com")
+    .size(512)
+    .default(avatars::Default::RoboHash)
+    .rating(avatars::Rating::G)
+    .build()
+    .image_url();
+assert_eq!(
+    url.as_str(),
+    "https://www.gravatar.com/avatar/836f82db99121b3481011f16b49dfa5fbc714a0d1b1b9f784a1ebbbf5b39577f?s=512&r=g&d=robohash"
+);
+```