Add instructions for editing documentation with the GitHub UI

[fellyph]

What is the problem?

The current contribution guide for documentation primarily assumes a workflow involving Git, the command line, and a local development environment. This can be a significant barrier for community members who are not developers, such as translators, writers, or those who simply want to fix a typo.

What is the proposed solution?

We should add a new section to our contribution guide that provides a step-by-step walkthrough for editing files directly through the GitHub web interface. This method requires no local setup and is much more accessible to a broader audience.

The guide should cover the entire end-to-end process:

1. Finding the correct documentation file in the repository.
2. Using the "Edit this file" (pencil icon) button.
3. Making changes in the web-based editor.
4. Writing a clear commit message and description.
5. Submitting the change as a new Pull Request.

This guide should be written with a non-technical audience in mind, using clear language and screenshots to illustrate each step.

Why is this important?

By providing an easier contribution path, we can:

• Lower the barrier to entry for new contributors.
• Increase community engagement from non-developers.
• Get more translations and typo fixes submitted.
• Make the project more inclusive and welcoming.