How to install:
1. Download and install Railcraft
2. Click Releases, then download the ZIP
3. Extract the folder from the ZIP 
4. Go to your Minecraft directory, instructions vary by launcher
5. Place the Railcraft 3D-master folder from the zip into the resourcepacks folder in your Minecraft directory.
6. Launch Minecraft
7. Go to Options > Resource Packs
8. Hover over Railcraft 3D and click the right arrow
9. Load a world and enjoy!