Update documentation

Author: pvdrz

book/src/lint_configuration.md

@@ -542,7 +542,8 @@ if no suggestion can be made.
 
 
 ### missing-docs-in-crate-items
-Whether to **only** check for missing documentation in `pub(crate)` items.
+Whether to **only** check for missing documentation in items visible within the current
+crate. For example, `pub(crate)` items.
 
 **Default Value:** `false` (`bool`)
 

clippy_lints/src/missing_doc.rs

@@ -36,7 +36,8 @@ declare_clippy_lint! {
 }
 
 pub struct MissingDoc {
-    /// Whether to only check for missing docs in `pub(crate)` items.
+    /// Whether to **only** check for missing documentation in items visible within the current
+    /// crate. For example, `pub(crate)` items.
     crate_items_only: bool,
     /// Stack of whether #[doc(hidden)] is set
     /// at each level which has lint attributes.