Improve about page
Improve about page

* rephrase some sentences
* add links to other documentation pages
* add warning about required configuration

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: Ic4dd2272ecb90268574968360e03136a5f91216b

GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners