This is a bit weird since it lives in the offers plugin, but it works
well. This should make runes much more approachable for people!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Any file in this directory which is executable and whose name only
consists of alphanumeric characters, space, '.', '-' or '_' will be
automatically loaded when lightningd starts (unless suppressed with
commandline options).