Improve Nginx Documentation

[markhughes]

Per a lot of older tickets, there is a lack of nginx docs:

• https://github.com/silverwind/droppy/issues/447
• https://github.com/silverwind/droppy/issues/446
• https://github.com/silverwind/droppy/issues/397
• https://github.com/silverwind/droppy/issues/315
• https://github.com/silverwind/droppy/issues/316
• https://github.com/silverwind/droppy/issues/360

We should try to cover all these topics relating to nginx.

[markhughes]

Installation guides page has been created, sub pages underway:

https://github.com/droppyjs/droppy/wiki/Installation-Guides

[markhughes]

Created here: https://github.com/droppyjs/droppy/wiki/Installation-Guide:-nginx