fix qnn install link (#3260) (#3271)

Summary:
Pull Request resolved: #3260

As title, the link was wrong...

Reviewed By: kirklandsign

Differential Revision: D56498322

fbshipit-source-id: 42708b5f7a634f1c01e05af4c897d0c6da54d724
(cherry picked from commit e9d7868)

examples/models/llama2/export_llama_lib.py

@@ -662,7 +662,8 @@ def _export_llama(modelname, args) -> str:  # noqa: C901
             quantizers = []
         except ImportError:
             raise ImportError(
-                "Please install the Qualcomm backend follwing https://pytorch.org/executorch/main/build-run-qualcomm.html"
+                "Please install the Qualcomm backend follwing "
+                "https://pytorch.org/executorch/main/build-run-qualcomm-ai-engine-direct-backend.html"
             )
 
         backend, quant_config = args.pt2e_quantize.split("_")