Update README.md

add how to manually build unitypackage

Author: inwoods

README.md

@@ -12,3 +12,16 @@ Requirements
 
 * [FBX SDK C# Bindings v0.0.1 or higher](https://github.com/Unity-Technologies/FbxSharp)
 
+Packaging
+---------
+
+**On OSX and Linux**
+
+```
+export PROJECT_PATH=~/Development/FbxExporters
+export UNITY3D_PATH=/Applications/Unity\ 5.6.1f1/Unity.app/Contents/MacOS/Unity
+export PACKAGE_NAME=FbxExporters
+export PACKAGE_VERSION=0.0.2
+
+"${UNITY3D_PATH}" -batchmode -projectPath "${PROJECT_PATH}" -exportPackage Assets/FbxExporters ${PROJECT_PATH}/${PACKAGE_NAME}_${PACKAGE_VERSION}.unitypackage -quit
+```