message: Add SwiftShader to BUILDING.md
diff: @@ -454,3 +454,17 @@ $ doxygen docs/doxygen/filament.doxygen
  ```
  Finally simply open `docs/html/index.html` in your web browser.
  +
  +## SwiftShader
  +
  +To try out Filament's Vulkan support with SwiftShader, first build SwiftShader and set the
  +`SWIFTSHADER_LD_LIBRARY_PATH` variable to the folder that contains `libvk_swiftshader.dylib`:
  +
  +```
  +git clone https://github.com/google/swiftshader.git
  +cd swiftshader/build
  +cmake .. && make -j
  +export SWIFTSHADER_LD_LIBRARY_PATH=`pwd`
  +```
  +
  +Next, go to your Filament repo and use the [easy build](#easy-build) script with `-t`.
  