Docs Overhaul

The docs are not perfect. Please edit this page with any suggestion you can have to improve them.

First of all, people struggle a lot with entities and that should be addressed. People also must understand the importance of input entities, because it matters a lot.

When getting started and moving to the next page, a lighter installation page could help, and move installing from source stuff later.

A suggestion for the new structure looks like this:

# Cheat Sheet
## Initialising Client
    from Telethon import TelegramClient 
    client = TelegramClient(...)
    with client:
        ...

## Entities
An entity object contains the following...
    id: ID of user
    username: Username of user
    access_hash: 

## Errors
`FloodWaitError`: Request made too often...

...

Another suggestion could look like the following:

# Quickstart
## Installation (brief)
## Creating a Client
## ???

# Dive In
## Installing from Source
## ???

We may also want to take inspiration from Rust's book.