latex-envs installation instructions

[sbenthall]

Related to #598

• Add to the installation instructions how to set up Jupyter with latex-envs in order to properly render the examples
• Add to HARK.utilities a script that tests whether this installation has been accomplished

[sbenthall]

May need to add it to requirements also, see: https://github.com/econ-ark/HARK/pull/598#issuecomment-605089480

[mnwhite]

Has this been handled? I feel like yes?