Update index.rst

[edwinnglabs]

Summary: Proposed to include Orbit in the related projects section

Intended Effect: N/A

How to Verify: N/A

Side Effects: N/A

Documentation: Just a change in the index.rst to add link of Orbit by uber

Reviewer Suggestions: Copyright and Licensing Orbit is under GPL3

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

Code: GPLv3 (http://opensource.org/licenses/GPL-3.0) Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[edwinnglabs]

@riddell-stan I re-create one here by pointing to the dev branch.

[ahartikainen]

Thanks for the PR. Orbit looks cool package.