Revert "git-diff: remove 9th example"

This reverts commit d31091d937.

pages/common/git-diff.md

@@ -27,6 +27,10 @@
 
 `git diff --summary {{commit}}`
 
+- Create a patch file:
+
+`git diff > {{target_file}}.patch`
+
 - Compare a single file between two branches or commits:
 
 `git diff {{branch_1}}..{{branch_2}} [--] {{path/to/file}}`