Documentation/notes: describe content of notes blobs

stripspace/text-based formatting kicks in when specifying the notes
content with -m or -F, or when an editor is used to edit the notes.
To binary-safely create notes from files, the following construct is
required:

    git notes add -C $(git hash-object -w <file>) <object>

Explain this trick (thanks, Johan!) in the manual.  Add an ordinary
example, too, to keep this esoteric one company.

Cc: Johan Herland <johan@herland.net>
Cc: Thomas Rast <trast@student.ethz.ch>
Cc: Jeff King <peff@peff.net>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-notes.txt

@@ -101,15 +101,20 @@ OPTIONS
 	Use the given note message (instead of prompting).
 	If multiple `-m` options are given, their values
 	are concatenated as separate paragraphs.
+	Lines starting with `#` and empty lines other than a
+	single line between paragraphs will be stripped out.
 
 -F <file>::
 --file=<file>::
 	Take the note message from the given file.  Use '-' to
 	read the note message from the standard input.
+	Lines starting with `#` and empty lines other than a
+	single line between paragraphs will be stripped out.
 
 -C <object>::
 --reuse-message=<object>::
-	Reuse the note message from the given note object.
+	Take the note message from the given blob object (for
+	example, another note).
 
 -c <object>::
 --reedit-message=<object>::
@@ -147,6 +152,37 @@ object, in which case the history of the notes can be read with
 `git log -p -g <refname>`.
 
 
+EXAMPLES
+--------
+
+You can use notes to add annotations with information that was not
+available at the time a commit was written.
+
+------------
+$ git notes add -m 'Tested-by: Johannes Sixt <j6t@kdbg.org>' 72a144e2
+$ git show -s 72a144e
+[...]
+    Signed-off-by: Junio C Hamano <gitster@pobox.com>
+
+Notes:
+    Tested-by: Johannes Sixt <j6t@kdbg.org>
+------------
+
+In principle, a note is a regular Git blob, and any kind of
+(non-)format is accepted.  You can binary-safely create notes from
+arbitrary files using 'git hash-object':
+
+------------
+$ cc *.c
+$ blob=$(git hash-object -w a.out)
+$ git notes --ref=built add -C "$blob" HEAD
+------------
+
+Of course, it doesn't make much sense to display non-text-format notes
+with 'git log', so if you use such notes, you'll probably need to write
+some special-purpose tools to do something useful with them.
+
+
 Author
 ------
 Written by Johannes Schindelin <johannes.schindelin@gmx.de> and

t/t3307-notes-man.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+test_description='Examples from the git-notes man page
+
+Make sure the manual is not full of lies.'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit A &&
+	test_commit B &&
+	test_commit C
+'
+
+test_expect_success 'example 1: notes to add an Acked-by line' '
+	cat <<-\EOF >expect &&
+	    B
+
+	Notes:
+	    Acked-by: A C Ker <acker@example.com>
+	EOF
+	git notes add -m "Acked-by: A C Ker <acker@example.com>" B &&
+	git show -s B^{commit} >log &&
+	tail -n 4 log >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'example 2: binary notes' '
+	cp "$TEST_DIRECTORY"/test4012.png .
+	git checkout B &&
+	blob=$(git hash-object -w test4012.png) &&
+	git notes --ref=logo add -C "$blob" &&
+	git notes --ref=logo copy B C &&
+	git notes --ref=logo show C >actual &&
+	test_cmp test4012.png actual
+'
+
+test_done