update prerequistes to jdk8 as several problems were reported

with jre-only installations on windows/mac os x.

installation.tex

@@ -9,18 +9,18 @@ \section{Prerequisites}
 met:
 
 \begin{itemize}
-  \item{Java Runtime Environment, 1.8 or later}
+  \item{Java Development Kit, 1.8 or later}
   \item{Supported Operating Systems: Windows, Linux, Mac OS X}
   \item{Memory requirements: $>=$ 512MB RAM}
   \item{(preferably broadband) Internet connection}
 \end{itemize}
 
 \subsection{Java}
 
-MGX requires a working Java Runtime Environment (JRE) to be installed on the computer. Typically,
+MGX requires a working Java Development Kit (JDK) to be installed on the computer. Typically,
 Java is already installed on most systems or can be obtained free of charge from\\
 
-\url{http://www.java.com/}.\\
+\url{http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html}.\\
 
 The installed Java version can be checked e.g. at\\
 
@@ -55,6 +55,6 @@ \subsection{Obtaining MGX}
     \url{ftp://ftp.cebitec.uni-bielefeld.de/pub/software/mgx/}.\\
 
 An installation isn't necessary, just unzip the file and start the software
-from the \texttt{bin/} subdirectory. Please check whether an updated version
+from the \texttt{bin/} subdirectory (Linux: \texttt{mgx\_gui}; Windows: \texttt{mgx\_gui64.exe}). Please check whether an updated version
 is available before reporting bugs.