git-reauthor: add page (#6651)

pages/common/git-reauthor.md

@@ -0,0 +1,17 @@
+# git reauthor
+
+> Change details about an author identity. Since this command rewrites the Git history, `--force` will be needed when pushing next time.
+> Part of `git-extras`.
+> More information: <https://github.com/tj/git-extras/blob/master/Commands.md#git-reauthor>.
+
+- Change an author's email and name across the whole Git repository:
+
+`git reauthor --old-email {{old@example.com}} --correct-email {{new@example.com}} --correct-name "{{name}}"`
+
+- Change the email and name to the ones defined in the Git config:
+
+`git reauthor --old-email {{old@example.com}} --use-config`
+
+- Change the email and name of all commits, regardless of their original author:
+
+`git reauthor --all --correct-email {{name@example.com}} --correct-name {{name}}`