Add How to contribute section with linter and editor setup

[urbanogilson]

This adds a new How to contribute section to the documentation, with:

• Instructions for installing Node.js dependencies using npm ci
• Details on how to run the linter (./lint or ./lint --fix)
• A note about recommended VSCode extensions from .vscode/extensions.json

  • takumii.markdowntable
    Helps edit and format markdown tables more easily. Great for keeping tables aligned and readable in README files.

  • yzhang.markdown-all-in-one
    A comprehensive markdown toolkit. Provides features like table of contents generation, shortcuts for formatting, and enhanced markdown preview.

  • streetsidesoftware.code-spell-checker
    Adds spell checking for markdown (and code comments). Helps catch typos in documentation and maintain a polished appearance.

  • editorconfig.editorconfig
    Reads .editorconfig settings to ensure consistent indentation, line endings, and other coding style rules across different editors and contributors.

[rvedotrc]

What's the reasoning here?

[rvedotrc]

Basically: do we want to make a conscious decision to standardise on en-GB, or en-US, or some other locale — or do we make a conscious decision that we don't care about the locales (and therefore spelling) that much?

[adamblanchard]

I write in en-GB by default (I'm from England) so you'll see that from me unless we decide otherwise. This repo is also called "programme" which I'm pretty sure is en-GB as well... :D

Saying that, we should probably choose/enforce one in the future, but at this point I don't have strong opinions. I'm approving it for now, with this change, regardless.

[rvedotrc]

(I edited the PR description, changing ./linter to ./lint)

[rvedotrc]

Not quite convinced about all these (yet), but they are only recommendations, so 🤷‍♀️