README: Document that local+global is not 100% accurate

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/README b/README
index 278ebb4e100e03fe237d041445665cff6b077f63..dc22589750237d84c4e475f7f20f0d9cd4c40d2a 100644 (file)
--- a/README
+++ b/README
@@ -398,6 +398,10 @@ suppressed with the &:warn directive.  The warning tags are:
        The same VARNAME was used both with and without an & prefix.
        This can be confusing.  Also, if you avoid this then you will
        get a warning iff you accidentally leave off a needed &.
+       The generation of this warning depends on scanning your
+       makefile for things that look like variable references, which
+       subdirmk does not do completely perfectly.  Exciting make
+       syntax may evade this warning, or require suppressions.
        (You can suppress this warning for a particular VARNAME with
        the &:local+global directive.)