Added some notes regarding ares_build.h

ares/README.cares

@@ -23,3 +23,41 @@ original ares.
 You'll find all c-ares details and news here:
 
         http://c-ares.haxx.se/
+
+
+NOTES FOR C-ARES HACKERS
+
+The following notes apply to c-ares version 7.6.1 and later.
+
+* The distributed ares_build.h file is only intended to be used on systems
+  which can not run the also distributed configure script.
+
+* The distributed ares_build.h file is generated as a copy of ares_build.h.dist
+  when the c-ares source code distribution archive file is originally created.
+
+* If you check out from CVS on a non-configure platform, you must run the
+  appropriate buildconf* script to set up ares_build.h and other local files
+  before being able of compiling the library.
+
+* On systems capable of running the configure script, the configure process
+  will overwrite the distributed ares_build.h file with one that is suitable
+  and specific to the library being configured and built, this new file is
+  generated from the ares_build.h.in template file.
+
+* If you intend to distribute an already compiled c-ares library you _MUST_
+  also distribute along with it the generated ares_build.h which has been
+  used to compile it. Otherwise the library will be of no use for the users of
+  the library that you have built. It is _your_ responsability to provide this
+  file. No one at the c-ares project can know how you have built the library.
+
+* File ares_build.h includes platform and configuration dependant info,
+  and must not be modified by anyone. Configure script generates it for you.
+
+* We cannot assume anything else but very basic compiler features being
+  present. While libcurl requires an ANSI C compiler to build, some of the
+  earlier ANSI compilers clearly can't deal with some preprocessor operators.
+
+* Newlines must remain unix-style for older compilers' sake.
+
+* Comments must be written in the old-style /* unnested C-fashion */
+