gitattributes.txt: document how to normalize the line endings

The instructions how to normalize the line endings should have been updated
as part of commit 6523728499 'convert: unify the "auto" handling of CRLF',
(but that part never made it into the commit).

Update the documentation in Documentation/gitattributes.txt and add
a test case in t0025.

Reported by Kristian Adrup
https://github.com/git-for-windows/git/issues/954

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

Documentation/gitattributes.txt

@@ -227,11 +227,9 @@ From a clean working directory:
 
 -------------------------------------------------
 $ echo "* text=auto" >.gitattributes
-$ rm .git/index     # Remove the index to force Git to
-$ git reset         # re-scan the working directory
+$ rm .git/index     # Remove the index to re-scan the working directory
+$ git add .
 $ git status        # Show files that will be normalized
-$ git add -u
-$ git add .gitattributes
 $ git commit -m "Introduce end-of-line normalization"
 -------------------------------------------------
 

t/t0025-crlf-auto.sh

@@ -152,4 +152,30 @@ test_expect_success 'eol=crlf _does_ normalize binary files' '
 	test -z "$LFwithNULdiff"
 '
 
+test_expect_success 'prepare unnormalized' '
+	> .gitattributes &&
+	git config core.autocrlf false &&
+	printf "LINEONE\nLINETWO\r\n"     >mixed &&
+	git add mixed .gitattributes &&
+	git commit -m "Add mixed" &&
+	git ls-files --eol | egrep "i/crlf" &&
+	git ls-files --eol | egrep "i/mixed"
+'
+
+test_expect_success 'normalize unnormalized' '
+	echo "* text=auto" >.gitattributes &&
+	rm .git/index &&
+	git add . &&
+	git commit -m "Introduce end-of-line normalization" &&
+	git ls-files --eol | tr "\\t" " " | sort >act &&
+cat >exp <<EOF &&
+i/-text w/-text attr/text=auto         LFwithNUL
+i/lf    w/crlf  attr/text=auto         CRLFonly
+i/lf    w/crlf  attr/text=auto         LFonly
+i/lf    w/lf    attr/text=auto         .gitattributes
+i/lf    w/mixed attr/text=auto         mixed
+EOF
+	test_cmp exp act
+'
+
 test_done