Document defaults for all the config lists

And add an imprecation in define_list_config_builder's doc comment do
do so in future for other invocations of the macro.

Add add the missing full stops.

crates/arti/src/logging.rs

@@ -66,7 +66,9 @@ impl LoggingConfig {
 type LogfileListConfig = Vec<LogfileConfig>;
 
 define_list_config_builder! {
-    /// List of logfiles to use, being built as part of the configuration
+    /// List of logfiles to use, being built as part of the configuration.
+    ///
+    /// The default is not to log to any files.
     pub struct LogfileListConfigBuilder {
         files: [LogfileConfigBuilder],
     }

crates/tor-circmgr/src/config.rs

@@ -186,7 +186,9 @@ fn default_preemptive_threshold() -> usize {
 type PredictedPortsList = Vec<u16>;
 
 define_list_config_builder! {
-    /// List of preemptive ports, being built as part of the configuration
+    /// List of preemptive ports, being built as part of the configuration.
+    ///
+    /// The default is `[80, 443]`.
     pub struct PredictedPortsListBuilder {
         pub(crate) ports: [u16],
     }

crates/tor-config/src/list_builder.rs

@@ -7,6 +7,7 @@
 ///
 /// `#[derive(Default, Clone, Deserialize)]` will be applied, but you can specify other attributes
 /// too.  You should supply a doc comment for the builder struct, as shown in the example.
+/// The doc comment should state the default value.
 ///
 /// The `built` clause specifies the type of the built value, and how to construct it.
 /// In the expression part, `things` (the field name) will be the resolved `Vec<Thing>`

crates/tor-dirmgr/src/authority.rs

@@ -45,7 +45,10 @@ impl Authority {
 pub(crate) type AuthorityList = Vec<Authority>;
 
 define_list_config_builder! {
-    /// List of authorities, being built as part of the configuration
+    /// List of authorities, being built as part of the configuration.
+    ///
+    /// The default is to use a set of compiled-in authorities,
+    /// whose identities and public keys are shipped as part of the Arti source code.
     pub struct AuthorityListBuilder {
         authorities: [AuthorityBuilder],
     }

crates/tor-guardmgr/src/fallback/set.rs

@@ -31,11 +31,14 @@ impl<T: IntoIterator<Item = FallbackDir>> From<T> for FallbackList {
 }
 
 define_list_config_builder! {
-    /// List of fallback directories, being built as part of the configuration
+    /// List of fallback directories, being built as part of the configuration.
     ///
     /// Fallback directories (represented by [`FallbackDir`]) are used by Tor
     /// clients when they don't already have enough other directory information to
     /// contact the network.
+    ///
+    /// The default is to use a set of compiled-in fallback directories,
+    /// whose addresses and public keys are shipped as part of the Arti source code.
     pub struct FallbackListBuilder {
         pub(crate) fallbacks: [FallbackDirBuilder],
     }