git-init: add --object-format example (#4888)

pages/common/git-init.md

@@ -7,6 +7,10 @@
 
 `git init`
 
+- Initialize a repository using SHA256 for object hashes (requires git version 2.29+):
+
+`git init --object-format={{sha256}}`
+
 - Initialize a barebones repository, suitable for use as a remote over ssh:
 
 `git init --bare`