git-diff-files: add page (#6896)

pages/common/git-diff-files.md

@@ -0,0 +1,20 @@
+# git diff-files
+
+> Compare files using their sha1 hashes and modes.
+> More information: <https://git-scm.com/docs/git-diff-files>.
+
+- Compare all changed files:
+
+`git diff-files`
+
+- Compare only specified files:
+
+`git diff-files {{path/to/file}}`
+
+- Show only the names of changed files:
+
+`git diff-files --name-only`
+
+- Output a summary of extended header information:
+
+`git diff-files --summary`