[fix] dead links in docuementation

[kyle-cochran]

Describe the bug

From a list compiled by Dhruv Jain

1.	OTSK Astrodynamics:
1.	https://open-space-collective.github.io/open-space-toolkit-astrodynamics/html/index.html 
1.	Documentation >>Python >> 404
2.	Tutorials >> C++ >> 404
3.	Tutorials >> C++ >> 404
4.	Contribution >> Contributing guide >> blank
5.	Dependencies >> Eigen >> http://eigen.tuxfamily.org/index.php “website seems to be down”

1.	README 
1.	Documentation >> Python >> “I do not believe the link is landing on the correct page”
2.	Tutorials >> C++ >> “sensor modelling example lacks description and comments to be easy to understand”
3.	Tutorials >> Python >> “no tutorial” -> route it to notebooks folder