Fixes broken API key generation link in readme (#68)

The previous link no longer exists/has been moved.

Author: sn0v

README.md

@@ -8,7 +8,7 @@ The Labelbox Python API offers a simple, user-friendly way to interact with the
 
 * Use Python 3.7 or 3.8.
 * Create an account by visiting http://app.labelbox.com/.
-* [Generate an API key](https://labelbox.com/docs/api/api-keys).
+* [Generate an API key](https://labelbox.com/docs/api/getting-started#create_api_key).
 
 ## Installation & authentication