update doc string and ret 1 on err

vice-speaker-rotator.py

@@ -7,6 +7,9 @@ import yaml
 
 # text appended to the end of generated emails
 email_body = """
+BBB room:
+[REDACTED]
+
 Full speaker schedule:
 https://cs.uwaterloo.ca/twiki/view/CrySP/SpeakerSchedule
 
@@ -22,7 +25,7 @@ def str_to_date(string_date):
         return date(*[int(s) for s in string_date.split('-')])
     except:
         print("invalid date: " + string_date)
-        sys.exit()
+        sys.exit(1)
 
 
 class CryspCalendar:
@@ -306,6 +309,8 @@ the following objects:
   practice_talks: a list of practice talks, each of the form:
     {date: _, note: _}
   half_practices: a list of half practice talks (format is the same)
+You cannot have multiple notes on the same day. If you have multiple objects
+with notes on the same day (likely two half_practices), their notes must match.
 ''',
                                      formatter_class=RawTextHelpFormatter)
     parser.add_argument('-y', '--yaml',