Updated landing page

[abrennan89]

Fixes #1881

Proposed Changes

• move Audience information to contributor docs
• Updated introduction / overview to remove fluff, additional words that don't add value or would be difficult for users to understand

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: abrennan89

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [abrennan89]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[evankanderson]

/lgtm

[vaikas]

It's complaining about newlines in pdf files...

  reviewdog: Reporting results for "EOF Newline"
  Error: [EOF Newline] reported by reviewdog 🐶
  Missing newline
  
  Raw Output:
  ./community/contributing/images/logo/rgb/knative-logo-rgb.ai:2518: Missing newline
  Error: [EOF Newline] reported by reviewdog 🐶
  Missing newline
  
  Raw Output:
  ./community/contributing/images/logo/cmyk/knative-logo-cmyk.ai:5594: Missing newline
  Error: Process completed with exit code 1.

vaikas-a01:eventing vaikas$ file !$
file ~/Downloads/knative-logo-rgb.ai
/Users/vaikas/Downloads/knative-logo-rgb.ai: PDF document, version 1.5

[vaikas]

Aaand, the istio-crds are nowhere to be found, so there's that which is nice...

Context "gke_knative-boskos-58_us-central1_e2e-cls" modified.
- Cluster is gke_knative-boskos-58_us-central1_e2e-cls
- Docker is gcr.io/knative-boskos-58/docs-e2e-img/7916
>> Bringing up Istio
>> Running Istio CRD installer
error: unable to read URL "https://raw.githubusercontent.com/knative-sandbox/net-istio/master/third_party/istio-stable/istio-crds.yaml", server reported 404 Not Found, status code=404

And indeed, they are not there (so not just a transient issue)
vaikas-a01:eventing vaikas$ curl -L 'https://raw.githubusercontent.com/knative-sandbox/net-istio/master/third_party/istio-stable/istio-crds.yaml' > /tmp/istio-crds.yaml
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 14 100 14 0 0 8 0 0:00:01 0:00:01 --:--:-- 8
vaikas-a01:eventing vaikas$ cat /tmp/istio-crds.yaml
404: Not Foundvaikas-a01:eventing vaikas$

[abrennan89]

/retest