Fix documentation

[bhavnicksm]

Currently, the documentation is extremely stale and requires us to do the following things:

• [x] Write an introduction about Nadir, the plan behind it, the meaning of the name and more
• [x] Add a table to show the papers/optimisers already implemented in Nadir
• [x] Show usage for a general optimiser in Nadir
• [x] provide how to install for Nadir
• [ ] Have some sort of imagery or emoji because the README looks kinda bland
• [ ] Add a coming soon optimisers to the table
• [ ] Add Acknowledgements to different implementations in the past
• [ ] Change citation

[nithinkr2000]

• [x] What is Nadir?
• [x] What changes are planned for the future?