Write documentation about dragon

[lintool]

@tuzhucheng

Write up documentation about using group-shared configs on dragon. Should probably go in docs/.

Also write up docs on how you set up the shared env, for when we need to upgrade later... for example, are we using a dedicated pytorch users? There should also be a canonical checkout of the data and models repo, right?

[tuzhucheng]

Currently I made a global conda installation at /anaconda3. For new dragon users, all they need to do to start using Conda & PyTorch with GPU is to add the following lines to their .bashrc:

export PATH="/anaconda3/bin:$PATH"
export LIBRARY_PATH="/usr/lib/nvidia-375"
export LD_LIBRARY_PATH=/opt/intel/mkl/lib/intel64:/usr/local/lib:/usr/local/cuda-8.0/lib64${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}

There is a global check-out of Castor-data and Castor-models at / that is owned by my own account. Maybe I can create a castor Linux group and add others to this group and change the permissions so anyone under this group have write access.

Currently any dragon user can install Python packages to the global environment. I should probably look into restricting this to a group of users as well.