Polish branches chapter

levels/branches/grow

@@ -0,0 +1,45 @@
+title = Branches grow with you!
+cards = checkout commit-auto branch branch-delete reset-hard
+
+[description]
+
+Note that there are two options to "travel to the end of a timeline":
+
+First, you can directly travel to the commit, like we've done it before.
+
+And second, you can travel to the branch label. In this case, when you make a new commit, the branch will grow with you, and still point at the end of the timeline, which is usually what we want!
+
+Let's try both of these!
+
+[setup]
+
+echo "You wrap the birthday present, and grab your concert ticket." > you
+git add .
+git commit -m "Evening preparations"
+echo "You go to the birthday party!" >> you
+git add .
+git commit -m "Go to the birthday"
+git branch birthday
+
+git checkout HEAD~1
+echo "You go to the concert!" > you
+git add .
+git commit -m "Go to the concert"
+git branch concert
+
+git checkout HEAD~1
+
+git branch -D main
+
+[win]
+
+# Travel directly to the last commit of the birthday timeline, make a change to 'you', and make a commit
+for commit in $(git cat-file --batch-check='%(objectname) %(objecttype)' --batch-all-objects | grep 'commit$' | cut -f1 -d' '); do
+    if test $(git rev-parse $commit^) = $(git rev-parse birthday); then
+        return 0
+    fi
+done
+return 1
+
+# Travel to the 'concert' branch, make a change to 'you', and a commit.
+git show concert^ | grep "Go to the concert"