To add an extra package to the stock warp distribution, you will need to add a few lines to the /pads/distro/<branch|trunk>/packages/Config.in file such as follows:
source "package/<extra package name>/Config.in"

For example:
source "package/classpath/Config.in"

Then run make menuconfig and you should see the package you just added.
# make menuconfig

Then run make
# make