Clarify some of the text, and fix inverted h2>h1 headings (which should have been h2>h3; we're still inconsistent across the guide as to whether the top level should be h1 or h2, but this clarifies which sections apply to what.)
Clarify some of the text, and fix inverted h2>h1 headings (which should have
been h2>h3; we're still inconsistent across the guide as to whether the top
level should be h1 or h2, but this clarifies which sections apply to what.)

BenJenkinson/nodatime,zaccharles/nodatime,malcolmr/nodatime,jskeet/nodatime,zaccharles/nodatime,BenJenkinson/nodatime,malcolmr/nodatime,zaccharles/nodatime,nodatime/nodatime,zaccharles/nodatime,nodatime/nodatime,zaccharles/nodatime,jskeet/nodatime,malcolmr/nodatime,zaccharles/nodatime,malcolmr/nodatime