Add docs for await_holding_invalid_types

Author: Jarcho

book/src/lint_configuration.md

@@ -364,7 +364,7 @@ Suppress lints whenever the suggested change would cause breakage for other crat
 
 
 ## `await-holding-invalid-types`
-
+The list of types which may not be held across an await point.
 
 **Default Value:** `[]`
 

clippy_config/src/conf.rs

@@ -416,6 +416,8 @@ define_Conf! {
     /// Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),
     /// Lint: AWAIT_HOLDING_INVALID_TYPE.
+    ///
+    /// The list of types which may not be held across an await point.
     (await_holding_invalid_types: Vec<DisallowedPath> = Vec::new()),
     /// DEPRECATED LINT: BLACKLISTED_NAME.
     ///