message: Update OSS build instructions
  Summary: getdeps.py changed slightly
diff: @@ -58,7 +58,7 @@ If on Linux or MacOS (with homebrew installed) you can install system dependenci
  git clone https://github.com/facebookincubator/mvfst.git
  # Install dependencies
  cd mvfst
  - sudo ./build/fbcode_builder/getdeps.py install-system-deps --recursive --install-prefix=$(pwd)/_build
  + sudo ./build/fbcode_builder/getdeps.py install-system-deps --recursive --install-prefix=$(pwd)/_build mvfst
  If you'd like to see the packages before installing them:
  