Brought documentation in sync with books/system/doc/acl2-doc.lisp.

git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1259 5d84a466-a78b-0930-a311-59b22171a541
Updated documentation to reflect the addition of community book books/demos/knuth-bendix-problem-1.lisp.

git-svn-id: http://acl2-devel.googlecode.com/svn/trunk@1260 5d84a466-a78b-0930-a311-59b22171a541