feat(www) : Add starters library to top navigation menu

[imedadel]

Description

The current navigation menu lacks a link to the starters library, which leads to using the browser's history or searching in google to find the page. This commit would add a link to starters library to make it easier to navigate to the page.

[wardpeet]

Tagging @fk @gatsbyjs/ecosystem @gatsbyjs/docs

[m-allanson]

Thanks @imedadel - I agree the starters could be more visible, however I'm going to close this PR for now. That's because making this change is more complex than it initially seems, and there's a future project that should improve this part of the site.

This change would need updates to the CSS to ensure the updated navigation fits at all browser widths - currently this code is different for the homepage and the rest of the site. In addition, there's no space at smaller breakpoints to include this in the mobile nav, so it won't be visible to all visitors.

There's a project to make several improvements to gatsbyjs.org, and making sure key parts of the site are discoverable is one of the aims there. See #14017 (although I think it's on hold for the moment).

For the above reasons I will close this. Thank you again for the PR and I hope to see more contributions from you in the future!