fix: fixed the broken links in docs

[aaryansinhaa]

Fixes #246

Had to add CONTRIBUTING.md, to introduce:
GET /CONTRIBUTING.md HTTP/1.1

and Renamed license.md -> LICENSE.md, to introduced:
"GET /LICENSE HTTP/1.1"

Also, wanted your suggestions on whether to add CONTRIBUTING to nav?

I also have that change ready if you want that.

nav:
  - Home: index.md
  - API Reference: api_reference/
  - Changelog: 'changelog.md'
  - Contributing: CONTRIBUTING.md
  - License: LICENSE.md

[rgaudin]

Great ; yes please add the contribution to menu and an entry in the changelog.