[Geoserver-devel] I do not find "WEB-INF/lib" folder‏

Thanks for the reply Jody Garnett. I did not understand, can you help me understand
I Download the source code of the page https://github.com/geoserver/geoserver/tree/master
and I have the following structure:
geoserver/bild
geoserver/data
geoserver/doc
geoserver/src
geoserver/.gitignore
geoserver/.travis.yml
geoserver/CONTRIBUIG.md
geoserver/README.md

I could already ejecuar the geoserver page and wish to add a new module as does the “Implementing a Wicket UI Extension”, but I find the “WEB-INF/lib” directory that is referenced.