Clarify module package documentation

docs/config.md

@@ -16,9 +16,9 @@ Precedence is:
 2. configuration file
 3. built-in defaults
 
-The implemented configuration overrides are `--units` and `--tz`. Output flags
-control report copies for the current command but do not change configuration
-files. Environment variables do not override configuration fields.
+The CLI configuration overrides are `--units` and `--tz`. Output flags control
+report copies for the current command but do not change configuration files.
+Environment variables do not override configuration fields.
 
 ## Minimal Config
 
@@ -177,8 +177,7 @@ snapshot exists and a threshold is crossed.
 ### `reports`
 
 `reports` optionally overrides the ordered deterministic modules declared by
-built-in report definitions. Omit a report entry to use its built-in module
-order.
+report definitions. Omit a report entry to use its default module order.
 
 Supported report keys are `daily`, `tomorrow`, `three_day`, `weekend`, and
 `storm`. Canonical report IDs such as `daily_today` and `daily_tomorrow` are
@@ -209,6 +208,10 @@ combinations, duplicate stanza names, and invalid options fail config loading.
 `key_messages`, `short_term`, and `long_term`. Empty or omitted `sections`
 includes all available AFD sections.
 
+The module registry accepts all module IDs documented in
+[Module Contract Internals](internal/module.md). Modules without builders are
+valid in composition but do not emit YAML stanzas.
+
 ## Secrets
 
 Configuration files should not contain raw secrets. Use `secrets.directory` to
@@ -224,6 +227,6 @@ notification, this allows a file such as
 - [examples/minimal-config.yml](../examples/minimal-config.yml): smallest
   useful config for generation and fetching.
 - [examples/config.yml](../examples/config.yml): production-oriented config
-  covering implemented fields.
+  covering maintained fields.
 
 Both example files are loaded by the config test suite.