documentation for the macro "add_permission"

Defines a permission vector for two types and a class.

It is defined in the file sets.m4.

m4 code:

define(`add_permission',
`ifdef(`permissionsX$1',
`define(`permissionsX$1',patsubst(patsubst(notmember(`
`$2'
',patsubst(`permissionsX$1',`
',`)notmember(`
`$2'
',')),`
$',)
`$2',^
,))',
`define(`permissionsX$1',`$2')')')