not sure if you are aware of this but there is already something implemented
which, more or less, does what you want. See Run menu Get php help.
Those entries are stored in shortcuts.xml file and can be modified to your needs.
(file is either available under %APPDATA%\notepad++ directory or
under installation directory - depends on your setup)
In addition there is a plugin called LanguageHelp which offers similar functionality.
Not 100% what you’ve asked for but maybe sufficient.
Cheers
Claudia