[PATCH v2] glossary: add definition for overlay

[Thomas Gummerer <t.gummerer@gmail.com>]

Add a definition for what overlay means in the context of git, to
clarify the recently introduced overlay-mode in git checkout.

Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---

v2 addresses Elijah's comments (thanks!), using the wording he
suggested in [*1*], which I agree is slightly better, as no-overlay
mode doesn't touch untracked files.

*1*: https://public-inbox.org/git/CABPp-BEv1taYym_084qVJj3-jkWWS9hKXZ=grrmH7PDUb5ASwA@mail.gmail.com/

 Documentation/glossary-content.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt
index 023ca95e7c..53df6ecb0a 100644
--- a/Documentation/glossary-content.txt
+++ b/Documentation/glossary-content.txt
@@ -287,6 +287,13 @@ This commit is referred to as a "merge commit", or sometimes just a
 	origin/name-of-upstream-branch, which you can see using
 	`git branch -r`.
 
+[[def_overlay]]overlay::
+	Only update and add files to the working directory, but don't
+	delete them, similar to how 'cp -R' would work.  This is the
+	default mode in a <<def_checkout,checkout>>.  In contrast,
+	no-overlay mode will also delete tracked files not present in
+	the source, similar to 'rsync --delete'.
+
 [[def_pack]]pack::
 	A set of objects which have been compressed into one file (to save space
 	or to transmit them efficiently).
-- 
2.21.0.474.g541d9dca55