Document the affected running phases of configuration directive?

[Yichun Zhang (agentzh)]

Hello!

It'll be great if the official nginx documentation documents the
affected request running phase of each configuration directive. For
example, proxy_pass affects the content phase while set_real_ip_from
affects the post-read and pre-access phases. This can help a lot when
the users try to combine directives of different modules and predict
their relative running order. Right now we have to look into the nginx
internals to be sure (either source code or debugging tools like gdb
and systemtap).

Thanks!
-agentzh