service-script-guide.md does not document the depends config option

[MiningMarsh]

The service-script-guide.md has a FIXME: regarding any potentially missing config options in the section documenting the depends function.

I was looking for a reference on the config option that tells openrc to re-evaluate it's dependency cache if a config file changes (I had forgotten what it was called), and couldn't find the documentation in that guide. I believe it should be added.

I use the config option in some openrc service files that call out to a shell program to determine their dependency list.