documentation should describe flume installation issues - in particular specifying JVM heap sizes

I've updated the faq with some basic detail:
"Why is Flume running out of memory?" http://github.com/cloudera/flume/wiki/FAQ
however the flume documentation (man page?) should provide this detail. Probably it should include other aspects of setting up flume, gotchas etc...

-------FAQ entry -------------
Ensure that you have provided the jvm with sufficient heap space. By default Flume starts the jvm with it's default heap allocation, which differs depending on the jvm version, the host type (os, 32/64 bit, etc...), total host memory available, as well as other issues.

The environment variable UOPTS can be used to pass additional jvm parameters when running Flume. e.g.

$ UOPTS="-Xms1g -Xmx2g" bin/flume node

which starts a flume node with an initial heap of one gig and a max heap of two gig. See "java -h" or "java -X" for more details on available jvm options.