Update broken readme link

usage-example.md

@@ -1,7 +1,7 @@
 In this guide, we will provide examples of using the high-level API, with less emphasis on
 the low-level implementation, since XKCP abstracts the low-level implementation from the user.
 
-Before proceeding with the usage example, please make sure that you have built the XKCP library as described in the [README](../README.markdown)
+Before proceeding with the usage example, please make sure that you have built the XKCP library as described in the [README](./README.markdown)
 and included it in your C/C++ project.
 
 # Hashing and extendable output functions (XOFs)