Broken Docker Dev Setup

Steps to reproduce

Follow the instructions of Develop using Docker documentation.

What happens?

Nginx errors:

• duplicate location "/media/__sized__/" in /etc/nginx/nginx.conf:124
• duplicate location "/media/attachments/" in /etc/nginx/nginx.conf:126
• "proxy_pass" cannot have URI part in location given by regular expression, or inside named location, or inside "if" statement, or inside "limit_except" block in /etc/nginx/nginx.conf:95
• MEDIA_ROOT variable is not defined

What is expected?

A working development environment with Docker.

Context

Affects develop branch.