slight next/forward link mismatch in documentation

[DanGrayson]

Here is a little package that can be used for testing the tree structure: Tree.m2.txt

Playing around with the results from that test package, it seems there is only one difference remaining between the info nodes and the html nodes: the last descendent of the top node has no "forward" node in info, but it links to the next root in html. The latter is the right way, since we expect to be able to read all the nodes of the package by pressing "forward" repeatedly.

See the discussion at https://github.com/Macaulay2/M2/pull/1454#issuecomment-691475911 and after.