DOCS-1616, DOCS-1655: clarifying hard/soft ulimit, adding note of nproc in RHEL/CentOS

Signed-off-by: Sam Kleinman <samk@10gen.com>
minor: edits
DOCS396, DOCS-1080, DOCS-1420, DOCS-1616 refactoring & updating production notes

prodnotes: updating with skot & samk's feedback

Conflicts:
	source/administration/production-notes.txt
	source/applications.txt
	source/core/update.txt

Signed-off-by: Sam Kleinman <samk@10gen.com>
toc: adding design notes to toc