Update _index.en.md

content/dev/build/osx/_index.en.md

@@ -6,11 +6,13 @@ weight: 21
 ```
 cd
 git clone https://github.com/microsoft/vcpkg
+cd vcpkg
 git checkout 2022.04.12
 ./bootstrap-vcpkg.sh
 brew install nasm yasm
 ./vcpkg install libvpx libyuv opus
 git clone https://github.com/rustdesk/rustdesk
 cd rustdesk
-VCPKG_ROOT=$HOME/vcpkg cargo run
+export VCPKG_ROOT=$HOME/vcpkg
+cargo run
 ```