Warning from index.rst re duplication LICENSE reference.

[tgkolda]

The following line:

pyttb/docs/source/index.rst

Line 17 in f491e1b

.. _`LICENSE`: ../../../LICENSE

Triggers the following error from sphynx:

C:\Users\TammyKolda\Documents\GIT Repos\pyttb\docs\source\index.rst:17: WARNING: Duplicate explicit target name: "license". [docutils]

I propose removing it.

This was probably introduced by #397. Apologies!

@dmdunla - I'm not sure of the best way to reference the license file. Let me know your opinion or feel free to fix directly however you see fit.

[dmdunla]

Fixed in PR #397