What is the scientific contribution or research aspect of the programming manual? With any research paper, be it journal or conference, the goal is to tackle a problem that has not been addressed and will be of significant value to the research community. You need to be specific about the contribution of the manual. If there is no valid scientific contribution, publishing it in a conference of journal does not make sense. However, if there is any algorithm that is novel, or if it is some simulator that you have implemented which can assist other researchers, then you can surely write it down as a paper so that other researchers can benefit from it.