Add paragraph on manual set-up

Signed-off-by: David Verhasselt <david@crowdway.com>

Add clarifying requirement of nginx 1.7.5 to authentication.md file.

Signed-off-by: David Verhasselt <david@crowdway.com>

Revert "Update authentication.md"

This reverts commit a79c28f4376fad333edd94e9b25211830e63abbd.

Add paragraph on manual set-up

docs/authentication.md

@@ -47,7 +47,6 @@ At this point, it's assumed that:
  * it's HIGHLY recommended that you get a certificate from a known CA instead of self-signed certificates
  * be sure you have stopped and removed any previously running registry (typically `docker stop registry && docker rm registry`)
 
-
 ### Setting things up
 
 Read again the requirements.
@@ -174,3 +173,13 @@ This is **advanced**.
 You will find [background information here](./spec/auth/token.md), [configuration information here](configuration.md#auth).
 
 Beware that you will have to implement your own authentication service for this to work (though there exist third-party open-source implementations).
+
+# Manual Set-up
+
+If you'd like to manually configure your HTTP server, here are a few requirements that are absolutely necessary for the docker client to be able to interface with it:
+
+- Each response needs to have the header "Docker-Distribution-Api-Version registry/2.0" set, even (especially) if there is a 401 or 404 error response. Make sure using cURL that this header is provided. Note: If you're using Nginx, this functionality is only available since 1.7.5 using the "always" add_header directive, or when compiling with the "more_set_headers" module.
+
+- A large enough maximum for client body size, preferrably unlimited. Because images can be pretty big, the very low default maximum size of most HTTP servers won't be sufficient to be able to upload the files.
+
+- Support for chunked transfer encoding.