added clone, create eclipse project and building

README.md

 # Exercise repository for Java Native Interface (JNI)
 
-This repository contains a "Hello World" example for using the Java Native Interface (JNI).
+At times, it is necessary to use native codes (C/C++) to overcome the memory management and performance constraints in Java. Java supports native codes via the Java Native Interface (JNI). This repository contains a "Hello World" example for using the JNI.
+
+# Prerequisites
+1. **Java Development Kit 8**
+2. **C/C++ Compiler**
+    * GCC compiler and Makefile ([Read "GCC and Make"](https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html)) **or**
+    * Cygwin or MinGW on Windows ([Read "How to Setup Cygwin and MinGW](https://www3.ntu.edu.sg/home/ehchua/programming/howto/Cygwin_HowTo.html)
+3. **Eclipse for Java Developers** with **C/C++ Development Tool (CDT) extension** installed ([Read "Eclipse CDT"](https://www3.ntu.edu.sg/home/ehchua/programming/howto/EclipseCpp_HowTo.html)).
+
+# Clone project
+```git clone https://es.technikum-wien.at/deinhofe/HelloJNI.git```
+
+# Create Eclipse project
+
+1. *File/New/Project*
+2. Select *General/Project* and click *Next*
+3. Unselect *Use default location* and browse to cloned diretory, click *OK*
+4. Enter *Project name* and click *Finish*
+
+# Build project
+
+Building the project involves two steps
+
+1. Building Java code
+    * Click on *Project/Build All*. This is not necessary if *Build Automatically* is selected.
+2. Building native code either on command line or using the configured Eclipse build targets
+    * Command line:```cd jni && make``` or
+    * Double click on *jni/Build Targets/all*
+
+
+