init: Supplement description to property action usage

Early set properties in DT or over the command-lines do not trigger
property-change events until boot stage.

Bug: 383738769
Test: After changing the action command line to tie to `early-boot`
event, the action is triggered earlier
Signed-off-by: Jack Chen <zenghuchen@google.com>
Merged-In: I000fcbf09f35cbaccc7517a3962fa4889b1d90be
Change-Id: I000fcbf09f35cbaccc7517a3962fa4889b1d90be