Update nginx docs

[svx]

Meta ticket for updating our nginx docs

• [ ] move install and configuration via buildout into a separate file
• [ ] update nginx config to modern and best practices
• [x] rewrite part about ssl, add good example
• [ ] ssl: add links to ssllabs
• [ ] add picture of a good ssllabs ranking
• [ ] ssl: add links and howto about configs and help pages
• [ ] /var/www is old style, mention also /srv
• [ ] better docs about certs also mention https://letsencrypt.org/
• [ ] fix old section "By using cookies" under "Session affinity"

[tkimnguyen]

I started by adding in an nginx SSL config, in https://github.com/plone/documentation/tree/update_nginx

[stevepiercy]

The section "By using cookies" under "Session affinity" is very old, and links to a no longer maintained repository for nginx sticky session module. The correct link is https://bitbucket.org/nginx-goodies/nginx-sticky-module-ng/overview, but since I'm not familiar with the process that is documented, I left it alone.

[tkimnguyen]

@stevepiercy I added that to the checklist - thx