Rework Readme

[Frijol]

Our readme has gotten really long, to the extent that it's probably not helpful anymore. I'm taking a look at how we can make it shorter and more up to date. Will keep notes here.

[Frijol]

Duplication of information. What's a Tessel/What's the Project About/How Can I Get Involved are really Website/Mission/Contributing. These sections should link to their respective pages instead of summarizing again. Relevant content from the readme should move into the individual pages.

[Frijol]

Contribute section is confusing, let's label it "Donate" or something– in an open source context, contribute is an ambiguous term

[Frijol]

"Read more" section– is this useful?

[Frijol]

"Reach out"– would it be more appropriate to link to tessel.io/community?

[Frijol]

"Current goals" – Is this the appropriate place to keep this information? Maybe yes. Maybe this should be the meat of the Readme.

[Frijol]

Ugh. Not sure I'm going about this well. What is it we need to convey in the Readme to this repo? Likely more useful to start with "What are people trying to learn when they visit this page?" rather than back-work from "why do we have all this". Any suggestions?

[Frijol]

Relevant: #355