update jre requirements (1.7 -> 1.8)

README

@@ -6,7 +6,7 @@ generated by Sun / Oracle, IBM, HP and BEA Java Virtual Machines. It
 is free software released under GNU LGPL.
 
 You can start GCViewer (gui) by simply double-clicking on gcviewer-1.3x.jar
-or running java -jar gcviewer-1.3x.jar (it needs a java 1.7 vm to run).
+or running java -jar gcviewer-1.3x.jar (it needs a java 1.8 vm to run).
 
 For a cmdline based report summary just type:
 java -jar gcviewer-1.3x.jar gc.log summary.csv [chart.png] [-t PLAIN|CSV|CSV_TS|SIMPLE|SUMMARY]
@@ -26,7 +26,11 @@ Supported verbose:gc formats are:
 - HP-UX JDK 1.2/1.3/1.4.x with the option -Xverbosegc
 - BEA JRockit 1.4.2/1.5/1.6 with the option -verbose:memory [-Xverbose:gcpause,gcreport] [-Xverbosetimestamp]
 
-Best results are achieved with: -Xloggc:<file> -XX:+PrintGCDetails -XX:+PrintGCDateStamps
+Best results are achieved with: -Xloggc:<file> -XX:+PrintGCDetails -XX:+PrintGCDateStamps.
+A few other options are supported, but most of the information generated is ignored by GCViewer
+(the javadoc introduction of 
+https://github.com/chewiebug/GCViewer/blob/master/src/main/java/com/tagtraum/perf/gcviewer/imp/DataReaderSun1_6_0.java
+shows the details).
 
 Hendrik Schreiber wrote GCViewer up to 1.29. What you are seeing here is based 
 on his very good work.