bpo-37504: Fix documentation build with texinfo builder (GH-14606)

bpo-37504: Fix documentation build with texinfo builder (GH-14606)

In the table model used by docutils, the `cols` attribute of `tgroup`
nodes is mandatory, see [1]. It is used in texinfo builder in [2].

[1]: https://www.oasis-open.org/specs/tm9901.htmGH-AEN348
[2]: https://github.com/sphinx-doc/sphinx/blob/v2.1.2/sphinx/writers/texinfo.pyGH-L1129

* Doc: Add texinfo support to the Makefile
(cherry picked from commit c3d679fd398f42a2e489fbe3dab17fac1fb2439c)

Co-authored-by: Dmitry Shachnev <mitya57@users.noreply.github.com>