Add Documentation for Each Model

[RupamGanguly46]

1. For each model, add instructions and screenshots in docs/.
2. Explain how to run, what parameters exist, and what each plot shows.

[zenitsu0509]

Hay please assign this issue to me

[Code-with-suraj-dotcom]

Hello, I’m interested in working on this issue for Hacktoberfest. May I be assigned to it so I can start contributing? Thank you!

[RupamGanguly46]

Hay please assign this issue to me

You can work on Linear Regression model's documentation after I merge PR's for that model👍🏻

[RupamGanguly46]

Hello, I’m interested in working on this issue for Hacktoberfest. May I be assigned to it so I can start contributing? Thank you!

Work on decision tree documentation only, after I merge PR for the ML model.