Apply suggestions from code review

Co-authored-by: wileyj <2847772+wileyj@users.noreply.github.com>

Author: Jiloc

stackslib/src/config/mod.rs

@@ -1292,11 +1292,15 @@ pub struct BurnchainConfig {
     /// The username for authenticating with the bitcoin node's RPC interface.
     /// Required if the bitcoin node requires RPC authentication.
     ///
+    /// Only relevant if [`NodeConfig::miner`] is `true`.
+    ///
     /// Default: `None`
     pub username: Option<String>,
     /// The password for authenticating with the bitcoin node's RPC interface.
     /// Required if the bitcoin node requires RPC authentication.
     ///
+    /// Only relevant if [`NodeConfig::miner`] is `true`.
+    ///
     /// Default: `None`
     pub password: Option<String>,
     /// Timeout duration, in seconds, for RPC calls made to the bitcoin node.