Add Knowledge Base article translation guide

[ChuanWeis]

Description

Adds a Knowledge Base article explaining how to translate Knowledge Base articles, including:

• copying an existing .en.md article and changing the language suffix
• preserving the category folder and front matter keys
• translating Markdown content while keeping links, images, and code blocks intact
• previewing with Hugo or Netlify deploy previews
• submitting the translated article in a pull request

This also replaces the Coming soon. placeholder in the existing contribution guide with a link to the new article.

Issues Resolved

Fixes #9

Preview Links

A Netlify preview should be available from the pull request checks once the deploy is created.

Expected generated paths from local build:

https://deploy-preview--navcoin-knowledgebase.netlify.com/general-support/translate-a-knowledge-base-article/
https://deploy-preview--navcoin-knowledgebase.netlify.com/general-support/contribute-to-the-knowledge-base/

Checklist

• Have you assigned/claimed the issues you've resolved in this pull request?
• Have the issues been moved to the QA column of the NavCoin Websites project?
• Have you checked there are no merge conflicts?
• Have you tested the changes work across both mobile and desktop?

Validation performed:

• git diff --check
• static Markdown/front matter/link checks
• Hugo Extended v0.55.6 build passed and generated both the new article page and the updated contribution article link

Note: I also tried Hugo Extended v0.161.1, but the existing theme/content does not build on that version due existing compatibility issues (.Hugo.Generator and an existing unparsable date in content/Stakeboxes/how to set up the navpi.en.md).