Documentation: mention that eol can change the dirty status of paths

When setting the `eol` attribute, paths can change their dirty status
without any change in the working directory. This can cause confusion
and should at least be mentioned with a remedy.

Signed-off-by: Ben Boeckel <mathstuf@gmail.com>
Reviewed-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: mathstuf

Documentation/gitattributes.txt

@@ -151,7 +151,10 @@ unspecified.
 
 This attribute sets a specific line-ending style to be used in the
 working directory.  It enables end-of-line conversion without any
-content checks, effectively setting the `text` attribute.
+content checks, effectively setting the `text` attribute.  Note that
+setting this attribute on paths which are in the index with CRLF line
+endings may make the paths to be considered dirty.  Adding the path to
+the index again will normalize the line endings in the index.
 
 Set to string value "crlf"::