Add a notice that only certain functions can print color escape codes

We emulate color escape codes on Windows by overriding printf, fprintf,
and fputs. Warn developers that these are the only functions that can be
used to print them.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

color.h

@@ -4,6 +4,11 @@
 /* "\033[1;38;5;2xx;48;5;2xxm\0" is 23 bytes */
 #define COLOR_MAXLEN 24
 
+/*
+ * IMPORTANT: Due to the way these color codes are emulated on Windows,
+ * write them only using printf(), fprintf(), and fputs(). In particular,
+ * do not use puts() or write().
+ */
 #define GIT_COLOR_NORMAL	""
 #define GIT_COLOR_RESET		"\033[m"
 #define GIT_COLOR_BOLD		"\033[1m"