[microNPU] Update Arm(R) Ethos(TM)-U55 NPU demo README (#9725)

- Update README.md to show config.cmake options when building from source

Change-Id: Iecc36d8bc889541b8b890de37d58052a46928a83

apps/microtvm/ethosu/README.md

@@ -43,6 +43,10 @@ If the demo is not run in the ci_cpu Docker container, then you will need the fo
 
 You will also need TVM which can either be:
   - Built from source (see [Install from Source](https://tvm.apache.org/docs/install/from_source.html))
+    - When building from source, the following need to be set in config.cmake:
+      - set(USE_ETHOSU ON)
+      - set(USE_MICRO ON)
+      - set(USE_LLVM ON)
   - Installed from TLCPack(see [TLCPack](https://tlcpack.ai/))
 
 You will need to update your PATH environment variable to include the path to cmake 3.19.5 and the FVP.