container: hledger-flow: paypal: add expenses description subaccount

- If expense description exists, add description as subaccount
  * This is consistent with all other legacy finance rules
    - Typically, legacy institutions provide a column for category type.
      Since PayPal doesn't provide that data, using the description will
      provide the needed information for granular (full view) reporting.

container/src/hledger-flow/accounts/paypal/paypal-shared.rules

@@ -70,6 +70,10 @@ if %direction ^OUT$
 if %direction ^OUT$
   account2 expenses:paypal:%subaccount:%currency_
 
+if %direction ^OUT$
+& %description_ [0-9a-z]
+  account2 expenses:paypal:platform:%description_:%currency_
+
 if %direction ^OUT$
 & %fees [1-9]
   account3 assets:paypal:%subaccount:%currency_