Docs: Undo heading name change to fix broken link

Docs: Undo heading name change to fix broken link

This commit reverts a chapter heading change, which had broken an
internal cross reference link, thus causing the HTML docs to fail to
build. In this case, it seems best to keep the older heading rather than
fix the link to it.

In general, we should be careful about changing any AsciiDoc
headings, since we currently rely on autogenerated section IDs when
making internal links, and changing a heading changes its ID. If a
heading is changed, then all links to it need to be changed accordingly.

This commit also corrects a heading underline.

Signed-off-by: Remington Steed <rjs7@calvin.edu>