You can generate searchable docs from a .gir (the thing that is built from scanning libvips and which in turn turn the typelib is made from) with g-ir-doc-tool, for example:

$ g-ir-doc-tool --language=Python -o ~/mydocs Vips-8.0.gir

Then to view them, either:

$ yelp ~/mydocs 

Or perhaps:

$ cd ~/mydocs 
$ yelp-build html .

To make HTML docs. This is an easy way to see what you can call in the library.