updated documentations

README.md

@@ -74,6 +74,8 @@ debugging purpose. No action or modification is made to the system unless you
 launch commands manually doing some.
 - **--chroot \<path\>**: Allows you to apply init.sh test or modification on a non
 running system, mounted in the given path.
+- **--cron**: execute init.sh in cron mode. Check cron subsystem documentation
+for more details.
 - **-l, --logfile**: Specify a custom name for the log file. Standard log file
 is named init-hostname-date-time.log in the log subdirectory. That file can also
 be customized using the LOGFILE environment variable.
@@ -254,6 +256,10 @@ export -f precheck_@template@
 Unexported template function will work but won't be available in the integrated
 debugging shell (see --shell option).
 
+An optionnal *cron_@template@* function allows you to define code that will be
+executed in cron mode. Check [cron documentation](./doc/cron.md) for more
+details.
+
 
 ## 3. Error code table
 
@@ -276,6 +282,7 @@ The following table is giving a list of error code with explanation:
 | 13        | Bad target file system              |
 | 14        | Impossible to chroot                |
 | 15        | Bad target filesystem/installation  |
+| 16        | Invalid options for cron mode       |
 | 50..100   | Error in module execution           |
 | 126       | Command exists but not executable   |
 | 127       | Command not found                   |