there actually are some instructions:

http://code.google.com/p/processing/wiki/ToolOverview#Where_to_put_Tools
http://processing.org/reference/tools/#libraries


or, if you made the tool based on the tool-template, you get a distribution package (after compiling the tool, which) also includes installation-instructions.

but indeed, theres nothing in the wiki like this (for libraries):
http://wiki.processing.org/w/How_to_Install_a_Contributed_Library

Thanks for that, the first link is probably the best solution although it's a shame there is not something on the wiki for users rather than developers.

or, if you made the tool based on the tool-template, you get a distribution package (after compiling the tool, which) also includes installation-instructions.
 

Found it - thanks again

@quarks: what tool was it you made?

The tool is a visual GUI builder for the G4P library.

It can be found here GUI builder

and you can see it in action in the video guides

Thank you very much!