Update README.md
diff --git a/caffe2/mobile/contrib/arm-compute/README.md b/caffe2/mobile/contrib/arm-compute/README.md
index 518c6c6..0fcf3aa 100644
--- a/caffe2/mobile/contrib/arm-compute/README.md
+++ b/caffe2/mobile/contrib/arm-compute/README.md
@@ -11,22 +11,24 @@
set ANDROID_NDK to /opt/android_ndk/xxx(e.g. /opt/android_ndk/android-ndk-r15c/)
setup toolchain:
+Let's say $PATH_TO_TOOLCHAIN is the directory you want to store the toolchain files.
+
arm
```
-rm -rf PATH_TO_TOOLCHAIN
-$ANDROID_NDK/build/tools/make_standalone_toolchain.py --arch arm --api 21 --install-dir PATH_TO_TOOLCHAIN
+rm -rf $PATH_TO_TOOLCHAIN
+$ANDROID_NDK/build/tools/make_standalone_toolchain.py --arch arm --api 21 --install-dir $PATH_TO_TOOLCHAIN
```
arm64
```
rm -rf PATH_TO_TOOLCHAIN
-$ANDROID_NDK/build/tools/make_standalone_toolchain.py --arch arm64 --api 21 --install-dir PATH_TO_TOOLCHAIN
+$ANDROID_NDK/build/tools/make_standalone_toolchain.py --arch arm64 --api 21 --install-dir $PATH_TO_TOOLCHAIN
```
add the toolchain path to .bashrc/.zshrc etc.
e.g.
```
-export PATH=$PATH:PATH_TO_TOOLCHAIN
+export PATH=$PATH:$PATH_TO_TOOLCHAIN/bin
```
use the build\_android.sh:
