git-show-index: add page (#5940)

pages/common/git-show-index.md

@@ -0,0 +1,12 @@
+# git show-index
+
+> Show the packed archive index of a Git repository.
+> More information: <https://git-scm.com/docs/git-show-index>.
+
+- Read an IDX file for a Git packfile and dump its contents to stdout:
+
+`git show-index {{path/to/file.idx}}`
+
+- Specify the hash algorithm for the index file (experimental):
+
+`git show-index --object-format={{sha1|sha256}} {{path/to/file}}`