added README.txt for ImageJ plugin

src/ImageJ/README.txt

+# Instructions for using building and running Pixel Rep ImageJ on Windows
+
+1. Install ImageJ
+
+Follow the instructions for your platform. Remember where it was installed.
+
+2. Install OpenCV
+
+Follow the instructions for your platform. Remember where it was installed.
+
+3. Find OpenCV Java bindings
+
+You need 2 files from the OpenCV package -- a JAR file and a shared library
+file. The JAR file is platform-independent, and is included here as
+opencv-2413.jar. The name of the shared library file will vary depending on the
+operating system. On Windows it is opencv_java2413.dll. 
+
+4. Copy the shared library to the ImageJ package
+
+Go to the root folder of your ImageJ installation. If they don't already exist,
+create folders lib and lib\x64 in this folder. Copy the OpenCV DLL to lib\x64.
+
+5. Recompile the plugin (optional)
+
+A compiled class file for the Pixel Rep plugin, Demo_Pixel_Replication.class,
+is included in the repository. It can be rebuilt with the following command:
+
+  javac -cp 'ij.jar;opencv-2413.jar' Demo_Pixel_Replication.java
+
+6. Copy the JAR files and class file to ImageJ
+
+The ImageJ root folder should have a plugins folder. The plugins folder should
+contain a Filters subfolder.  Copy these 3 files to plugins\Filters:
+
+* ij.jar opencv-2413.jar Demo_Pixel_Replication.class
+
+7. Test the plugin
+
+Run the following steps
+
+* Start (or restart) ImageJ 
+* Open a binary image
+* Choose Plugins/Filters/Demo Pixel Replication from the top menu