git-range-diff: add page (#5701)

pages/common/git-range-diff.md

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+# git range-diff
+
+> Compare two commit ranges (e.g. two versions of a branch).
+> More information: <https://git-scm.com/docs/git-range-diff>.
+
+- Diff the changes of two individual commits:
+
+`git range-diff {{commit_1}}^! {{commit_2}}^!`
+
+- Diff the changes of ours and theirs from their common ancestor, e.g. after an interactive rebase:
+
+`git range-diff {{theirs}}...{{ours}}`
+
+- Diff the changes of two commit ranges, e.g. to check whether conflicts have been resolved appropriately when rebasing commits from `base1` to `base2`:
+
+`git range-diff {{base1}}..{{rev1}} {{base2}}..{{rev2}}`