doc: git-rebase: start with an example

Start with an example that mirrors the example in the `git-merge` man
page, to make it easier for folks to understand the difference between a
rebase and a merge.

Signed-off-by: Julia Evans <[email protected]>

Author: jvns

Documentation/git-rebase.adoc

@@ -16,6 +16,29 @@ SYNOPSIS
 
 DESCRIPTION
 -----------
+Transplant a series of commits onto a different starting point.
+
+For example, imagine that you have been working on the `topic` branch in this
+history, and you want to "catch up" to the work done on the `master` branch.
+
+------------
+          A---B---C topic
+         /
+    D---E---F---G master
+------------
+
+You want to transplant the commits you made on `topic` since it diverged from
+`master` (i.e. A, B, and C), on top of the current `master`.  You can do this
+by running `git rebase master` while the `topic` branch is checked out.  If you
+want to rebase `topic` while on a different branch, `git rebase master topic` is a
+short-cut for `git switch topic && git rebase master`.
+
+------------
+                  A'--B'--C' topic
+                 /
+    D---E---F---G master
+------------
+
 If `<branch>` is specified, `git rebase` will perform an automatic
 `git switch <branch>` before doing anything else.  Otherwise
 it remains on the current branch.
@@ -58,32 +81,6 @@ that caused the merge failure with `git rebase --skip`.  To check out the
 original `<branch>` and remove the `.git/rebase-apply` working files, use
 the command `git rebase --abort` instead.
 
-Assume the following history exists and the current branch is "topic":
-
-------------
-          A---B---C topic
-         /
-    D---E---F---G master
-------------
-
-From this point, the result of either of the following commands:
-
-
-    git rebase master
-    git rebase master topic
-
-would be:
-
-------------
-                  A'--B'--C' topic
-                 /
-    D---E---F---G master
-------------
-
-*NOTE:* The latter form is just a short-hand of `git checkout topic`
-followed by `git rebase master`. When rebase exits `topic` will
-remain the checked-out branch.
-
 If the upstream branch already contains a change you have made (e.g.,
 because you mailed a patch which was applied upstream), then that commit
 will be skipped and warnings will be issued (if the 'merge' backend is