;update CLI usage texts

hledger/Hledger/Cli/Commands/Balance.txt

@@ -426,7 +426,47 @@ Budget performance in 2017/11/01-2017/12/31:
 ----------------------++----------------------------------------------------
                       ||      0 [              0]       0 [              0] 
 
-For more examples, see Budgeting and Forecasting.
+For more examples and notes, see Budgeting.
+
+Budget report start date
+
+This might be a bug, but for now: when making budget reports, it's a
+good idea to explicitly set the report's start date to the first day of
+a reporting period, because a periodic rule like ~ monthly generates its
+transactions on the 1st of each month, and if your journal has no
+regular transactions on the 1st, the default report start date could
+exclude that budget goal, which can be a little surprising. Eg here the
+default report period is just the day of 2020-01-15:
+
+~ monthly in 2020
+  (expenses:food)  $500
+
+2020-01-15
+  expenses:food    $400
+  assets:checking
+
+$ hledger bal expenses --budget
+Budget performance in 2020-01-15:
+
+              || 2020-01-15 
+==============++============
+ <unbudgeted> ||       $400 
+--------------++------------
+              ||       $400 
+
+To avoid this, specify the budget report's period, or at least the start
+date, with -b/-e/-p/date:, to ensure it includes the budget goal
+transactions (periodic transactions) that you want. Eg, adding
+-b 2020/1/1 to the above:
+
+$ hledger bal expenses --budget -b 2020/1/1
+Budget performance in 2020-01-01..2020-01-15:
+
+               || 2020-01-01..2020-01-15 
+===============++========================
+ expenses:food ||     $400 [80% of $500] 
+---------------++------------------------
+               ||     $400 [80% of $500] 
 
 Nested budgets