docs: organize sections and pages

[ldez]

Just a bit a reorganisation of the pages of the documentation.

• Split "Usage" section into a "Welcome" section and a "Usage" section.
• Move "Performance" page into the "Product" section.
• Split "Roadmap" page into a "Roadmap" page and a "Changelog" page.
• Change the order of the questions in the FAQ.
• Move version policy and deprecation cycle from "Install" to "Roadmap".
• Remove disabled linters from "Quick Start"

Sidebar Before

.
├── Introduction
├── Usage
│   ├── Install
│   ├── Quick Start
│   ├── Integrations
│   ├── Linters
│   ├── Configuration
│   ├── False Positives
│   ├── Performance
│   └── FAQ
├── Product
│   ├── Roadmap
│   ├── Thanks
│   ├── Trusted By
│   └── GitHub
├── Contributing
│   ├── Quick Start
│   ├── Workflow
│   ├── Architecture
│   ├── New Linters
│   ├── Debug
│   ├── FAQ
│   └── This Website
└── Plugins
    ├── Module Plugin System
    └── Go Plugin System

Screenshot Before

Sidebar After

.
├── Introduction
├── Welcome
│   ├── Install
│   ├── Quick Start
│   ├── Integrations
│   └── FAQ
├── Usage
│   ├── Configuration
│   ├── Linters
│   └── False Positives
├── Product
│   ├── Thanks
│   ├── Trusted By
│   ├── Changelog
│   ├── Roadmap
│   ├── Performance
│   └── GitHub
├── Contributing
│   ├── Quick Start
│   ├── Workflow
│   ├── Architecture
│   ├── New Linters
│   ├── Debug
│   ├── FAQ
│   └── This Website
└── Plugins
    ├── Module Plugin System
    └── Go Plugin System

Screenshot After

FAQ TOC Before

FAQ TOC After

[ldez]

@bombsimon do you have an opinion on this one?

[bombsimon]

LGTM! No strong feelings for this but might want to not put too much effort into the web page if we hope to get to a replacement in the somewhat near future.

This is a nice short term change though! 👍🏼