feat: setup project documentation

[ajndkr]

As the project grows, there is a strong need for a docs page for new (and existing) users to find information which might be too verbose to add to the repo README.

For the first version, we can add:

• getting started
• api reference
• tutorial 1: deploy basic llm chain
• tutorial 2: deploy chains with vector store / retriever
• tutorial 3: deploy custom chains

Acceptance Criteria

• study https://readthedocs.org/
• publish docs on https://readthedocs.org/

[ajndkr]

@rogalvil any recommendations towards this?

[rogalvil]

@ajndkr Honestly, I don't have any recommendations. I don't have much experience with documentation.