docs : fix the link to llama.h (#14293)

Author: david20571015

docs/build.md

@@ -1,6 +1,6 @@
 # Build llama.cpp locally
 
-The main product of this project is the `llama` library. Its C-style interface can be found in [include/llama.h](include/llama.h).
+The main product of this project is the `llama` library. Its C-style interface can be found in [include/llama.h](../include/llama.h).
 
 The project also includes many example programs and tools using the `llama` library. The examples range from simple, minimal code snippets to sophisticated sub-projects such as an OpenAI-compatible HTTP server.