Update $DEMO_APP definition

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: luffy-yu

docs/source/backends-qualcomm.md

@@ -290,7 +290,7 @@ The model, inputs, and output location are passed to `qnn_executorch_runner` by
 
 ### Run [Android LlamaDemo](https://github.com/meta-pytorch/executorch-examples/tree/main/llm/android/LlamaDemo) with QNN backend
 
-`$DEMO_APP` refers to the root of executorch android demo root, i.e., the directory containing `build.gradle.kts`.
+`$DEMO_APP` refers to the root of the executorch android demo, i.e., the directory containing `build.gradle.kts`.
 
 ***Step 1***: Rebuild ExecuTorch AAR