Add jhat example with larger memory limit.

pages/common/jhat.md

@@ -9,3 +9,7 @@
 - Analyze a heap dump, specifying an alternate port for the http server:
 
 `jhat -p {{port}} {{dump_file.bin}}`
+
+- Analyze a dump letting jhat use up to 8GB RAM (2-4x dump size recommended):
+
+`jhat -J-mx8G {{dump_file.bin}}`