Update blurb on main page w/ more about DN's role in Nebula

[jasikpark]

https://nebula.defined.net/docs#about-defined-networking

nebula-docs/docs/intro.md

Lines 108 to 128 in a2ba32c

	## History
	After several years of internal development, Nebula was open-sourced by Slack in 2019. Read the announcement posted on
	Slack's Engineering blog.
	[Introducing Nebula, the open source global overlay network from Slack](https://slack.engineering/introducing-nebula-the-open-source-global-overlay-network-from-slack/)
	By early 2020, the project had over 4,000 stars on GitHub and it was being adopted by organizations of all sizes.
	As of December 2021, Nebula continues to power Slack's global overlay network of over 50,000 production hosts.
	[Read Nebula's Release Notes on GitHub](https://github.com/slackhq/nebula/releases) to learn about additions and changes
	to the project.
	## About Defined Networking
	Nebula's creators, Ryan Huber and Nate Brown, founded Defined Networking in 2020 to focus on Nebula development and to
	broaden the adoption of overlay networking in organizations.
	As of early 2021, Slack continues to be a primary sponsor of the Nebula open source project. Defined Networking is
	publishing this official documentation with their support.

[jasikpark]

or ig ## About Defined Networking could be a sub-section of ## History?