Update the comments for package installer commands

These commands are for the communication between the installer and the
update binary (edify interpreter). Update the comments in sync with the
codes.

Change-Id: I7390f022b1447049a974b0b45697ef1d2e71d4e0
diff --git a/install.cpp b/install.cpp
index 662f81c..c7d382f 100644
--- a/install.cpp
+++ b/install.cpp
@@ -88,7 +88,7 @@
     //            fill up the next <frac> part of of the progress bar
     //            over <secs> seconds.  If <secs> is zero, use
     //            set_progress commands to manually control the
-    //            progress of this segment of the bar
+    //            progress of this segment of the bar.
     //
     //        set_progress <frac>
     //            <frac> should be between 0.0 and 1.0; sets the
@@ -107,6 +107,18 @@
     //        ui_print <string>
     //            display <string> on the screen.
     //
+    //        wipe_cache
+    //            a wipe of cache will be performed following a successful
+    //            installation.
+    //
+    //        clear_display
+    //            turn off the text display.
+    //
+    //        enable_reboot
+    //            packages can explicitly request that they want the user
+    //            to be able to reboot during installation (useful for
+    //            debugging packages that don't exit).
+    //
     //   - the name of the package zip file.
     //