fastboot: update-super help text

Bug: 393978923
Test: th
Change-Id: I7d51eab0ba27a487b853037a62b0884726da58dd
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 156dc3b..a3d8b98 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -588,6 +588,12 @@
             "                            Delete a logical partition with the given name.\n"
             " resize-logical-partition NAME SIZE\n"
             "                            Change the size of the named logical partition.\n"
+            " update-super NAME\n"
+            "                            Merges changes to the super partition metadata.\n"
+            "                            If a merge isn't possible (for example, the format\n"
+            "                            on the device is an unsupported version), then this\n"
+            "                            command fails. An optional wipe parameter overwrites\n"
+            "                            the device's metadata, rather than performing a merge.\n"
             " snapshot-update cancel     On devices that support snapshot-based updates, cancel\n"
             "                            an in-progress update. This may make the device\n"
             "                            unbootable until it is reflashed.\n"