FPv2: add comment about nuance of fuzzy fingerprinting (commaai#28465)

add comment describing this nuance of fuzzy fingerprint function

Author: sshane

selfdrive/car/fw_versions.py

@@ -91,6 +91,8 @@ def match_fw_to_car_fuzzy(fw_versions_dict, log=True, exclude=None):
         elif candidate != candidates[0]:
           return set()
 
+  # Note that it is possible to match to a candidate without all its ECUs being present
+  # if there are enough matches. FIXME: parameterize this or require all ECUs to exist like exact matching
   if len(matched_ecus) >= 2:
     if log:
       cloudlog.error(f"Fingerprinted {candidate} using fuzzy match. {len(matched_ecus)} matching ECUs")