readme: note CLI spec location and state/backup defaults

- In development: the CLI command structure is specified in
  Documentation/cli.md
- Config: daemon state and database backups default to ~/.config/rpn
  (backups in its backups/ subdirectory), overridable in config

readme.md

@@ -40,6 +40,9 @@ not speed or efficiency.
   from embedded migrations (schema_migrations table).
 - Config: TOML file (see config.template.toml), loaded via
   --config flag or $RUSTYRPN_CONFIG. Real config files are gitignored.
+  Daemon state (pidfile, logs) and database backups default to
+  ~/.config/rpn (backups in its backups/ subdirectory); both are
+  overridable in config.
 - Serialization: serde / serde_json.
 - Logging: tracing (level via RUST_LOG).
 - CSV/TSV files: csv crate; non-standard raw-export dates are parsed by
@@ -263,6 +266,7 @@ Use a test-driven-development inspired approach, specifically the following work
 nothing yet…
 ### In development
 * cli
+    * command structure specified in Documentation/cli.md
     * ingest tab-separated .txt files containing transactions from automated gas station into a MariaDB
     * create invoices from data in database
 ### Future / planned