doc: fix mistakes in prog guide

- Remove wrong document description:
The Programmer’s Guide intro is not the Release Notes.

- Fix heading of section which only deals with Tx queues configuration.

- Fix wrong verbatim text paragraphs:
Reduce the indentation of these paragraphs since they are not part of the
verbatim block.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: John McNamara <john.mcnamara@intel.com>