[racket-dev] docs don't make sense

http://docs.racket-lang.org/drracket/extending-drracket.html?q=teachpack#(part._teachpacks)

-----
As an example, the following teachpack provides a lazy cons
implementation. To test it, be sure to save it in a file named
"lazycons.ss".

...

Then, in this program:

...

the list all-nums is bound to an infinite list of ascending numbers.
-----

1. It's not clear why one must "be sure to" save it in that particular name.

2. The above docs don't say to actually *install* the Teachpack.

Presumably #2 meant to reference "lazycons.ss".  But the "be sure to"
is misleading (the name is meaningless).

Also, the .ss should probably be .rkt.