create_prior_diststats: add a couple of FIXMEs

- to remind me to update for the < 2 instruments case

gstlal-inspiral/bin/gstlal_inspiral_create_prior_diststats

@@ -93,6 +93,7 @@ def parse_command_line():
 	process_params = dict(options.__dict__)
 
 	options.instrument = set(options.instrument)
+	# FIXME:  reduce min to 1
 	if not options.instrument or len(options.instrument) < 2:
 		raise ValueError("must specify at least two distinct --instrument's")
 

gstlal-inspiral/bin/gstlal_ll_inspiral_create_prior_diststats

@@ -91,6 +91,7 @@ def parse_command_line():
 	seglistdict, horizon_history = parse_segment_and_horizon(options)
 
 	options.instruments = frozenset(seglistdict)
+	# FIXME:  generalize to < 2
 	if len(options.instruments) < 2:
 		raise ValueError("must specify at least two distinct instrument")