Overhaul documentation structure and content

Nobody has claimed this yet.

Is your feature request related to a problem? Please describe.
By far the biggest obstacle new and existing users are experiencing when either trying to onboard or to develop within nf-core is the suboptiomal documentation that has accumulated relatively organically over many years ^1.

Despite some improvements with the website replacement, many people are still finding the project documentation difficult to navigate and find the information they need - also finding critical information missing and/or out of date.

Describe the solution you'd like
We should a big overhaul the structure and content of the project documentation to ensure it is effective in giving a good user- and developer-experience.

We should target both users and developers, and follow a proper framework such as Diataxis (https://diataxis.fr) to ensure it is easy for people to add and extend documentation in a ordered and structured way.

[!NOTE]
This issue actually spans more than just the website, but putting it here due to the below - once we have a better plan an RFC will be made

Additional context
This includes many outstanding issues we have on this repo including:

Start by reviewing the linked website issues and the Diataxis framework to map the documentation gaps affecting users and developers. The issue notes that an RFC should follow once there is a better plan; done means producing an agreed documentation structure and content-overhaul plan that addresses the identified gaps.

Written by the indexing model from the issue text.

Description

Contributor guide

First steps

Research direction

Assessment