Add warning about NVIDIA cards.

README

@@ -10,10 +10,11 @@ Dependencies:
 
 Basic *nix build instructions:
 	To build with GPU mining support:
-	Install AMD APP sdk, latest version - there is no offiical place to
+	Install AMD APP sdk, latest version - there is no official place to
 	install it so just keep track of where it is if you're not installing
 	the include files and library files into the system directory.
-	
+	(Do NOT install the ati amd sdk if you are on nvidia)
+
 	./autogen.sh	# only needed if building from git repo
 	CFLAGS="-O3 -Wall -march=native" ./configure
 	or if you haven't installed the ati files in system locations:
@@ -33,6 +34,7 @@ Basic WIN32 build instructions (on Fedora 13; requires mingw32):
 	
 Native WIN32 build instructions (on mingw32, on windows):
 	Install AMD APP sdk, latest version
+	(Do NOT install the ati amd sdk if you are on nvidia)
 	Install mingw32
 	Install libcurl, copy libcurl.m4 into /mingw/share/aclocal
 	Run: