core: Add note about reply route

[xkaraman]

Add note regarding reply_route, that last command should be a return or a successful method so the reply is relayed.

[miconda]

Thanks, it can be merged.

And probably it should be tested if negative return in a branch route is dropping the branch or not.

[xkaraman]

Yep, i will try to test it also on branch routes and note it if nessecary!