A fix of Internal links for SN Reader's Guide

Sending warm wishes from the wilds of British Columbia. :wolf: :unicorn:

RE: SuttaCentral

The link at the top of the page for the Great Book, goes to the “Book of the Six Sense Fields,” which is missing from those top -of-the-page chapter options.

And the link for the Textual History goes to the Great Book.

Easy to fix. :slight_smile: