Update NGINX Ingress Documentation

[rikatz]

We've had a lot of improvements in the last few days, as the following:

• Port in redirect #151
• Add support for custom header sizes #150
• Add flag to allow switch off the update of Ingress status #149
• https://github.com/kubernetes/ingress/blob/85733700ecd3ae31ee9531f8f13dba816c249629/controllers/nginx/rootfs/etc/nginx/template/nginx.tmpl#L223

I don't think those parameters are documented, so I'm opening this issue to document them.

Anyone can collaborate on this one (actually, we can make a checklist with this issue), so all the latest options from Ingress Controller can be used and tested.

[porridge]

s/Configuration/Documentation/?