Revert "Remove now-unusable 'setcon' command."

Temporarily revert because device isn't booting.

This reverts commit 7b15ac99f3bfef33c82ea109487c99a77b41ebfb.

Change-Id: Ice986bac62e20c70f7bedf1744a617b97392ae8c
diff --git a/init/readme.txt b/init/readme.txt
index 6b9c42d..84afd11 100644
--- a/init/readme.txt
+++ b/init/readme.txt
@@ -252,6 +252,11 @@
 rmdir <path>
    Calls rmdir(2) on the given path.
 
+setcon <seclabel>
+   Set the current process security context to the specified string.
+   This is typically only used from early-init to set the init context
+   before any other process is started.
+
 setprop <name> <value>
    Set system property <name> to <value>. Properties are expanded
    within <value>.