Pull up following revision(s) (requested by sevan in ticket #153):

share/man/man1/cd.1: revision 1.10
share/man/man1/cd.1: revision 1.9

Direct reader to shell documentation generally, rather than csh(1)
specifically.

Mention variables OLDPWD and PWD.

Move the text that explains that cd(1) is a shell built-in to the very
beginning of the description where it can be seen prominently.

Improve formatting.

(martin)