doc: cf: update cash account inference description for 1.25

hledger/Hledger/Cli/Commands/Cashflow.md

@@ -1,17 +1,30 @@
 cashflow, cf\
 This command displays a cashflow statement, showing the inflows and
-outflows affecting "cash" (ie, liquid) assets.
+outflows affecting "cash" (ie, liquid, easily convertible) assets.
 Amounts are shown with normal positive sign, as in conventional
 financial statements.
 
 _FLAGS
 
-The "cash" accounts shown are those accounts declared with the `Cash`
-type, or otherwise all accounts under a top-level `asset` account
-(case insensitive, plural allowed) which do not have `fixed`,
-`investment`, `receivable` or `A/R` in their name.
+"Cash" assets are those accounts which are (or whose parents are) 
+declared as `Cash` by an account directive, like this:
 
-Example:
+```journal
+account some:liquid:asset    ; type:C
+```
+
+Or if there are no such declarations, all accounts
+
+- under a top-level `asset` account (case insensitive, plural allowed) 
+- with some variation of `cash`, `bank`, `checking` or `saving` in their name.
+
+More precisely: all accounts matching this case insensitive regular expression:
+
+`^assets?(:.+)?:(cash|bank|che(ck|que?)(ing)?|savings?|currentcash)(:|$)`
+
+and their subaccounts.
+
+An example cashflow report:
 ```shell
 $ hledger cashflow
 Cashflow Statement