This is just an initial documentation. Needs improvement.
There are two ways plugin are added to the menu. First, if an algorithm is listed in the default_menu.xml file, which is found in the configuration/ directory of a CIShell tool, it is added in the place specified by the default_menu.xml file. Secondly, if an algorithm is not listed in this file, but has specified a menu_path property in the algorithm.properties file, the menu manager CIShell service will add it to the appropriate menu, as described in the by the menu_path property's value (for example, Analysis/additions will place an algorithm on the bottom of the Analysis menu).