Update welcome page

[Hans5958]

I'm clearing the backlog one at the time.

• Update getting started section to reflect latest circumstances (need to click puzzle icon, new version, update images to high quality)
• Add section to pin the extension

@WorldLanguages please improve the wording (if needed)

[Hans5958]

Preview

[Samq64]

Could /addons be linked somewhere? I think that's a better way for new users to discover new addons right now.

[Hans5958]

If I have #259 implemented that this is probable, but as the page is limited, linking to /addons would not add much value to the user.