init: add 'enable <service>' to negate "service <service>... disabled"

enable <servicename>
   Turns a disabled service into an enabled one as if the service did not
   specify disabled in the rc file.
   It will also start the service if needed.

Bug: 14472973
Change-Id: Id0b49cc687a2bc74f6f92e066c617724cc94908d
Signed-off-by: JP Abgrall <jpa@google.com>
diff --git a/init/readme.txt b/init/readme.txt
index 42a09cb..613a9e9 100644
--- a/init/readme.txt
+++ b/init/readme.txt
@@ -178,6 +178,16 @@
 domainname <name>
    Set the domain name.
 
+enable <servicename>
+   Turns a disabled service into an enabled one as if the service did not
+   specify disabled.
+   If the service is supposed to be running, it will be started now.
+   Typically used when the bootloader sets a variable that indicates a specific
+   service should be started when needed. E.g.
+     on property:ro.boot.myfancyhardware=1
+        enable my_fancy_service_for_my_fancy_hardware
+
+
 insmod <path>
    Install the module at <path>