add documentation for Kakoune

[Techatrix]

The zigtools website should have documentation on how to use ZLS with Kakoune.

The following steps should be documented if possible and applicable:

• kakoune-lsp installation
• in-editor configuration (also per-project config)
  • set explicit path to ZLS executable
  • set explicit path to Zig executable
  • mention build on save
• code action on save (source.fixAll and source.organizeImports)
• format on save
• inlay hints

The structure and wording of the documentation should be in line with exiting editors that have been documented on the website.