Reorganize the Docs navigation

**👋 This is a proposal for reorganizing the navigation on the NetlifyCMS docs site. The goal is to make it easier for users to find the guidance they need.**

## A proposal for a new navigation structure

In short, there are a few things I was trying to do here:
- group guidance around the decisions users are trying to overcome
- make it easier to find help around the challenge you're facing
- keep naming of the docs consistent with the components and code

### Better packaging
As an editor, there are different types of decsions I need to make when setting up NetlifyCMS, each with it's own effect on the way my site will grow over time. Some of these decisions are foundational to integrating with your platform, others affect how your editors will develop habits and workflows over time. Setting up a CMS is important work and if done well, it can have a huge impact on the confidence of the team that is responsible for the site day-to-day.

To get there, I think we need to group pages under headings that reflect the decisions that users would need to consider and the challenges they're trying to overcome when setting up NetlifyCMS.

### Each decision area should have
- **An overview** that helps to orient people, explains the terminology and how to think about these settings and the effect they'll have on your site.
- **A list of pages** for this decision area _(for the most part, these are already there)_
- **Examples** – a page where people from the community can leave
- **Community discussion** – a link to a cooresponding page in the community https://community.netlify.com/c/netlify-cms/31

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# NetlifyCMS Docs Navigation
https://www.netlifycms.org/docs/intro/

### Quick Start
- Introduction
- Releases
- Start With A Template
- Add To Your Site

### Configuration
- Overview
- Configuration Options
- Update the CMS Version
- Beta Features! ---------------- _👈 more on unpacking this at a later point_
- Examples
- Community discussion

### Workflow
- Overview
- Deploy Preview Links
- Open Authoring
- Examples
- Community discussion

### Backend
- Overview
- Git Gateway
- Bitbucket
- GitHub
- GitLab
- Test
- External OAuth Clients
- Examples
- Community discussion

### Media
- Overview
- Cloudinary
- Netlify Large Media
- Uploadcare
- Examples
- Community discussion

### Collections
- Overview
- Collection Types
- Examples
- Community discussion

### Fields
- Overview
- Boolean
- Code
- Date
- DateTime
- File
- Hidden
- Image
- List
- Map
- Markdown
- Number
- Object
- Relation
- Select
- String
- Text
- Examples
- Community discussion

### Platform Guides
- Overview
- Gatsby
- Hugo
- Jekyll
- NextJS
- Nuxt
- Middleman

### Customization
- Overview
- Creating Custom Widgets
- Creating Custom Previews
- Examples
- Community discussion

### Contributing
- Overview
- Contributor Guide
- Writing Style Guide
- Architecture