[AntoninKns]

Reorganizes the documentation following the Diátaxis framework as suggested in #122 . The documentation/index.md is split into tutorials, how-to guides, reference and explanation pages, with the MkDocs navigation grouped to match.

I did not find any guideline prohibiting the use of LLMs for contributions to this repository, that is why I took the liberty to use Claude Code to help me apply the changes. I read the documentation, did an initial manual split then completed it automatically using Claude Code. I built it and reviewed it locally, tested the links and everything seems fine. I generated the PR description using Claude Code, but entirely reviewed it and edited it manually.

This PR only modifies structure to make review easier. The text is moved verbatim, not rewritten except minor adjustments mentioned below. If this suits you, I will make a further PR with some language changes to follow the Diátaxis framework more strictly.

Structure changes

• Layout: index.md is split into tutorials/, how-to/, reference/ and explanation/.
  • Tutorial: the "A Quick Example" section only.
  • How-to: setup, configuration, working with HDX objects (datasets, resources, showcases, organizations, users, locations, vocabularies), activity streams, statistics, pipeline state and examples.
  • Reference: the breaking changes list. The mkapi API pages sit alongside it in the nav.
  • Explanation: information, default configuration for facades, and history.
• Navigation (documentation/mkdocs.yaml): Five top-level groups. How-to Guides is grouped into Set up, Configure, Work with HDX objects (Datasets and Resources sub-groups), Other tools and Examples. API Documentation comes before Breaking Changes under Reference.
• documentation/index.md: Now the summary plus a link list that mirrors the nav (the old anchor-based table of contents is gone).
• .gitignore: Ignores the MkDocs site/ build output.

Changes beyond moving text

• Each page has a single # heading, retitled in imperative style (e.g. "Obtain your API Key"). The nav labels match them.
• Cross-page references broken by the split now link to the right pages: framework.md → install, tutorial → API key, resource operations → dataset resources, changelog → tags. Two anchors were rewritten as relative links.
• Removed the tutorial's broken demo GIF (HTTP 404). It was already broken before this PR. The original Markdown is kept in an HTML comment.
• Renamed the directory operate-datasets.md/ to operate-datasets/.