Front page content

[imphil]

Front page: https://github.com/lowRISC/lowrisc-web/blob/master/site/layouts/index.html

• [x] Insert content and images into the highlight columns
• [x] Insert content into the larger "featurette" rows below.
• [x] Remove ecosystem diagram
• [x] Add remaining 3 content blobs
• [x] remove "view details" buttons
• [x] make sure we have a GitHub link/button somewhere
• [x] Fix distortion / cutaway in top image

The highlight columns look best if they all are roughly the same height (number of lines).

[LaurieJ]

Adjusted content. Not the most amazing layout but we'll have new featurettes soon so maybe good enough for now.

[GregAC]

Potential PR for github link/button in header here: https://github.com/lowRISC/lowrisc-web/pull/27

[imphil]

all open issues fixed.

@LaurieJ Is the homepage OK like this?

[imphil]

Got LGTM from Laura on chat, closing.