some docs fixes for x86_64

COPYRIGHT

@@ -19,6 +19,9 @@ The implementation of DES for crypt (src/misc/crypt.c) is Copyright ©
 1994 David Burren. It is licensed under a BSD license compatible with
 the GNU LGPL.
 
+The x86_64 port was written by Nicholas J. Kain. See individual files
+for their copyright status.
+
 All files which have no copyright comments are original works
 Copyright © 2005-2011 Rich Felker, the main author of this library.
 The decision to exclude such comments is intentional, as it should be

INSTALL

@@ -5,12 +5,9 @@ A quick-and-simple guide to installing musl:
 STEP 1: Configuration
 
 Edit config.mak to override installation prefix, compiler options,
-etc. as needed. The defaults should be okay for trying out musl with
-static linking only. The only arch supported at present is i386. If
-you're on an x86_64 machine, you can add -m32 to the compiler options
-to build a working 32bit musl. In this case you will also need to add
--m32 in two locations in the generated tools/musl-gcc script if you
-intend to use it.
+target architecture, etc. as needed. Currently supported archs are
+i386 and x86_64. Otherwise, the defaults should be okay for trying out
+musl with static linking only.
 
 DO NOT set the prefix to /, /usr, or even /usr/local unless you really
 know what you're doing! You'll probably break your system such that