doc: check for absence of the form --[no-]parameter

doc: check for absence of the form --[no-]parameter

For better searchability, this commit adds a check to ensure that parameters
expressed in the form of `--[no-]parameter` are not used in the
documentation.  In the place of such parameters, the documentation should
list two separate parameters: `--parameter` and `--no-parameter`.

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>