Add STDIO documentation template. Signed-off-by: Marek Vasut <marex@denx.de> Cc: Marek Vasut <marek.vasut@gmail.com> Cc: Tom Rini <trini@ti.com> [trini: Fix DOCBOOKS line as we don't have linker_lists yet] Signed-off-by: Tom Rini <trini@ti.com>