include/README: remove "hacking" advice, not the right place

... style and point the compiler's include path to the directory holding the

curl subdirectory. It makes it more likely to survive future modifications.

NOTE FOR LIBCURL HACKERS

* If you check out from git on a non-configure platform, you must run the

  appropriate buildconf* script to set up files before being able of compiling

  the library.

* 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 */

To figure out how to do good and portable checks for features, operating

systems or specific hardwarare, a very good resource is Bjorn Reese's

collection at https://sourceforge.net/p/predef/wiki/

The public curl include files can be shared freely between different platforms

and different architectures.