Merge pull request progit#1424 from Smaug123/hash-note

Author: ben

book/10-git-internals/sections/objects.asc

@@ -257,8 +257,14 @@ $ echo 'First commit' | git commit-tree d8329f
 fdf4fc3344e67ab068f836878b6c4951e3b15f3d
 ----
 
+
+[NOTE]
+====
 You will get a different hash value because of different creation time and author data.
+Moreover, while in principle any commit object can be reproduced precisely given that data, historical details of this book's construction mean that the printed commit hashes might not correspond to the given commits.
 Replace commit and tag hashes with your own checksums further in this chapter.
+====
+
 Now you can look at your new commit object with `git cat-file`:
 
 [source,console]