[PATCH] More documentation, minor cleanup in kdump.txt

Added clarification on the root device format to be used for second kernel,
as well as specifying initrd if drivers are built as modules.

Signed-off-by: Kishore Sampathkumar <kishore.sampathkumar@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>