Link to the doxygen documentation is broken in software-design.md

[icepolarizer]

In doc/software-design.md, there is:

As we saw while code spelunking, the source code is also documented using doxygen. You may wish to attempt to match items from these design documents to some of the code.

But the link to the doxygen document is missing.
And so is this link : The story for a first SIGCOMM paper.

This issue is not urgent, but I think somebody should fix this.