Added Nginx to serving arches, with config

[ekansa]

brief description of changes

This provides some instruction on using Gunicorn and Nginx, with an example Nginx config that describes how to compress css, javascript, etc.

issues addressed

#267

further comments

I am using more or less the same Nginx config in my Docker deployed Arches instance, so It seems to work. I'm not an Nginx guru, so I'm sure it could be better, but it's nice to provide a working starting point for people wanting to deploy Arches with Nginx.

You can view the update here;
https://arches.readthedocs.io/en/nginx_m/deployment/serving-arches-with-apache/#configure-nginx

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This box must be checked

• the PR branch was originally made from the base branch

This box should be checked

• after these changes the docs build locally without error

This box should only be checked you intend to follow through on it (we can do it on our end too)

• I will cherry-pick all commits in this PR into other branches that should have them after this PR is merged

[mradamcox]

Great! Good to have NGINX in here finally.