Revamp front page

[waxlamp]

We should rework the content on the "front page". What's there now is a great starter (thank you, @banesullivan!) but now I think we can look at how to make it connect with readers more effectively.

Some suggestions to get the discussion going:

1. We should remove or significantly rework the Core Values section. The mention of D&A's values hasn't been socialized to the public yet, and it's too general for inclusion here. Instead, I think we should have a prose section that gives a general, high-level overview of what this docs site is and who it's for, along with a link to important documentation, such as the "what is girder" article.
2. "Key Advantages" sounds too proposalesque or salesmanish to me. This plays into the general mission of our putting this documentation site together. One of our audiences is people who know us and know the Girder brand, but are confused by our history of doing different things under the brand. Explaining what Girder 4 is very briefly and describing our general approach to working with customers might be better here.
3. Instead of salesmanship, perhaps just a simple CTA to contact us for more information or a consultation would be good.

@zachmullen, @jeffbaumes, @banesullivan, please add your thoughts and then we can generate some concrete issues (trackable from this issue in a list).