The `expire` sub-command of `git multi-pack-index` will never expire
`.keep` packs, regardless of whether or not any of their objects were
selected in the MIDX.

This has always been the case since 19575c7c8e (multi-pack-index:
implement 'expire' subcommand, 2019-06-10), which came after cff9711616
(multi-pack-index: prepare for 'expire' subcommand, 2019-06-10), when
this documentation was originally written.

Signed-off-by: Taylor Blau <redacted>
---
 Documentation/git-multi-pack-index.txt | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index b4a2378cd8..11e6dc53e3 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt

@@ -71,8 +71,9 @@ verify::
 
 expire::
 	Delete the pack-files that are tracked by the MIDX file, but
-	have no objects referenced by the MIDX. Rewrite the MIDX file
-	afterward to remove all references to these pack-files.
+	have no objects referenced by the MIDX (with the exception of
+	`.keep` packs). Rewrite the MIDX file afterward to remove all
+	references to these pack-files.
 
 repack::
 	Create a new pack-file containing objects in small pack-files

-- 
2.37.0.1.g1379af2e9d