Add documentation using jsdoc

[NehmatH]

The purpose of adding the documentation

The Kitsu client does not currently have a documentation which makes it, as it develops, difficult to read and understand. To make sure the code is readable and easy to maintain, it's good practice to add documentation to it.
This is what was done here using JSDoc.

The reason behind the choice of JSDoc

The use of JSDoc was based on its popularity as an API documentation generator for JavaScript. It is one of the most recommended tools for its ease of use and high customization, and it shows in the resulting website.

JSDoc works in the following way: the developer adds documentation comments directly to the source code which JSDoc will scan. It will then generate an HTML documentation website.

The current state of the documentation

A detailed documentation has been added to the existing code in the project, but it is still a work in progress.