Add content to placeholder descriptions on ecosystem landing page (#9583)
Add content to placeholder descriptions on ecosystem landing page (#9583)

- Added content for the descriptions for all three content areas (plugins, starters, external resources)

<img width="1549" alt="screen shot 2018-10-30 at 7 10 30 pm" src="https://user-images.githubusercontent.com/3461087/47758106-92634b80-dc77-11e8-9fa5-17b63ea9ef81.png">

ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,mingaldrichgan/gatsby,0x80/gatsby,0x80/gatsby,mingaldrichgan/gatsby