Update README.md

README.md

@@ -11,18 +11,32 @@ Unity Visual Effect Graph.
 ![gif](https://i.imgur.com/jPluUSJ.gif)
 
 
-System Requirements
+System requirements
 -------------------
 
 - Unity 2019.3
 - High Definition Render Pipeline 7.1
 
-Frequently Asked Questions
---------------------------
+How to export a volume from Houdini
+-----------------------------------
 
-#### How do I generate vector field data?
+Firstly, you have to install `Unity_VFX_Tools.hda` to your project. Download
+and import it from the [VFXToolbox] repository.
 
-You can use Houdini and a plugin called [VFXToolbox] to generate a vector
-field file (.vf). [VFXToolbox] is provided from Unity and available on GitHub.
+[VFXToolbox]:
+  https://github.com/Unity-Technologies/VFXToolbox/tree/master/DCC-Tools%7E/Houdini
 
-[VFXToolBox]: https://github.com/Unity-Technologies/VFXToolbox
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+
+You can export a `.vf` file using Volume Exporter SOP. There are a few things to
+take care of:
+
+- It only supports the standard volume. If you're using a VDB volume, you have
+  to convert it to a standard one.
+- It only supports uniformly sized volume (x size == y size == z size). You may
+  have to resize it before exporting.
+- The default wrap mode of `.vf` file is "repeat." It should be changed to
+  "clamp" when using a distance field volume.
+
+For details, please see the example Houdini project contained in the
+[`Houdini`](Houdini) directory.