fix guile manual

[Developers list for Guile, the GNU extensibility library]

there is a link on page 
https://www.gnu.org/software/guile/manual/guile.html#rnrs-base
... (see R6RS Base library 
<https://www.gnu.org/software/guile/manual/r6rs.html#Base-library> in...
            [https://www.gnu.org/software/guile/manual/r6rs.html#Base-library]
That doesn't work. 
I don't know how to submit path, so just wrote this message.