git-diff-index, git-diff-tree: add page (#11234)

* git-diff-index, git-diff-tree: add page

---------

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/git-diff-index.md

@@ -0,0 +1,20 @@
+# git diff-index
+
+> Compare the working directory with a specific commit or tree object.
+> More information: <https://git-scm.com/docs/git-diff-index>.
+
+- Compare the working directory with a specific commit:
+
+`git diff-index {{commit}}`
+
+- Compare a specific file or directory in working directory with a commit:
+
+`git diff-index {{commit}} {{path/to/file_or_directory}}`
+
+- Compare the working directory with the index (staging area) to check for staged changes:
+
+`git diff-index --cached {{commit}}`
+
+- Suppress output and return an exit status to check for differences:
+
+`git diff-index --quiet {{commit}}`