[PATCH 3/4] glossary: add reachability bitmap description

["Philip Oakley via GitGitGadget" <gitgitgadget@gmail.com>]

From: Philip Oakley <philipoakley@iee.email>

Signed-off-by: Philip Oakley <philipoakley@iee.email>
---
 Documentation/glossary-content.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt
index a9e69949a4e..6302df90563 100644
--- a/Documentation/glossary-content.txt
+++ b/Documentation/glossary-content.txt
@@ -500,6 +500,12 @@ exclude;;
 	<<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
 	that they contain.
 
+[[def_reachability_bitmap]]reachability bitmaps::
+	Reachability bitmaps store information about the set of objects in
+	a packfile, or a multi-pack index (MIDX). A repository may have at
+	most one bitmap. The bitmap may belong to either one pack, or the
+	repository's multi-pack index (if it exists).
+
 [[def_rebase]]rebase::
 	To reapply a series of changes from a <<def_branch,branch>> to a
 	different base, and reset the <<def_head,head>> of that branch
-- 
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