;doc: update CLI usage texts

hledger/Hledger/Cli/Commands/Balance.txt

@@ -348,6 +348,14 @@ Examples:
     "total","VEA","36.00"
     "total","VHT","294.00"
 
+Here is how --layout currently affects the various output formats:
+
+         txt   csv   html   json   sql
+  ------ ----- ----- ------ ------ -----
+  wide   Y     Y     Y             
+  tall   Y     Y     Y             
+  bare   Y     Y     Y             
+
 Sorting by amount
 
 With -S/--sort-amount, accounts with the largest (most positive)