chore(website): Announce Gatsby plugin 4.0.0

[talves]

Summary

Blog post to Announce 4.0.0 Gatsby Plugin

Test plan

Review on build.

A picture of a cute animal (not mandatory but encouraged)
📝

[netlify]

Preview proposed changes to the CMS demo site in the link below:

Built with commit d8f6ac2

https://deploy-preview-2313--cms-demo.netlify.com

[netlify]

Preview proposed changes to netlifycms.org in the link below:

Built with commit d8f6ac2

https://deploy-preview-2313--netlify-cms-www.netlify.com

[erquhart]

Looks good, ready to merge when you are, Tony - good to go?

[talves]

Just added the Media Libraries section, so can we get a build of the site to review?

[erquhart]

Here 'tis: https://deploy-preview-2313--netlify-cms-www.netlify.com/blog/2019/05/netlify-cms-gatsby-plugin-4-0-0

[talves]

LGTM

[erquhart]

Sorry for the delay here @talves - finally had a sec to run through this, took the opportunity to add in the bigger picture of the Gatsby plugin. Stretched the scope a bit, but that story isn't told anywhere, so this gives us a good place to tell it. Hopefully folks searching to understand the whole Gatsby/Netlify CMS thing will make it here.

I think context will help folks better grasp why this all matters. Let me know if you have any thoughts.