Add reference for attributes in function parameters

Author: c410-f3r

src/attributes.md

@@ -50,6 +50,7 @@ Attributes may be applied to many things in the language:
 * [Generic lifetime or type parameter][generics] accept outer attributes.
 * Expressions accept outer attributes in limited situations, see [Expression
   Attributes] for details.
+* [Function][functions] parameters accept outer attributes.
 
 Some examples of attributes:
 

src/items/functions.md

@@ -17,7 +17,7 @@
 > &nbsp;&nbsp; _FunctionParam_ (`,` _FunctionParam_)<sup>\*</sup> `,`<sup>?</sup>
 >
 > _FunctionParam_ :\
-> &nbsp;&nbsp; [_Pattern_] `:` [_Type_]
+> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup>\ [_Pattern_] `:` [_Type_]
 >
 > _FunctionReturnType_ :\
 > &nbsp;&nbsp; `->` [_Type_]
@@ -282,3 +282,4 @@ attributes macros.
 [`link_section`]: ../abi.md#the-link_section-attribute
 [`no_mangle`]: ../abi.md#the-no_mangle-attribute
 [external_block_abi]: external-blocks.md#abi
+[_OuterAttribute_]: ../attributes.md