init: Update readme.txt to reflect recent changes to init

Best practice for services that reside on the system, vendor, and odm
partitions is to have a corresponding init .rc file in the
/{system,vendor,odm}/etc/init directory, which contains its service
entry and any related actions.

Change-Id: I26204f9a0f09ce8069f3791ccd9ee61d164a048f
1 file changed