quadruped_model boilerplate

[grassjelly]

Hi,

First of all thanks for making this repo available to the public. I was looking at the issues and it seems that a lot of potential users encounter the same build problem related to missing quadruped_model package. I understand that the package may contain some proprietary information about ANYmal but is there any boilerplate that we can use in order to model arbitrary robots. I'm looking at interfacing this with https://github.com/chvmp/champ and hopefully make this more accessible to the community.

Thank you!