Doc fix for `MOZ_NON_PARAM`

Attributes.h.patch

diff --git a/mfbt/Attributes.h b/mfbt/Attributes.h
--- a/mfbt/Attributes.h
+++ b/mfbt/Attributes.h
@@ -571,17 +571,22 @@
  *   or via functions called from the constructor body.
  * MOZ_IS_CLASS_INIT: Applies to class method declarations. Occasionally the
  *   constructor doesn't initialize all of the member variables and another function
  *   is used to initialize the rest. This marker is used to make the static analysis
  *   tool aware that the marked function is part of the initialization process
  *   and to include the marked function in the scan mechanism that determines witch
  *   member variables still remain uninitialized.
  * MOZ_NON_PARAM: Applies to types. Makes it compile time error to use the type
- *   in parameter without pointer or reference.
+ *   in parameter without pointer or reference. Visual Studio does not permit
+ *   extra alignment requirements on parameters, so passing a type by value that
+ *   uses alignas(T) causes an error (C2719). Types like Vector and Maybe use
+ *   alignas on the inline buffers that hold their values; marking them with
+ *   this attribute helps us catch attempts to pass them earlier on other
+ *   platforms, without waiting for a Windows build to fail.
  * MOZ_NON_AUTOABLE: Applies to class declarations. Makes it a compile time error to
  *   use `auto` in place of this type in variable declarations.  This is intended to
  *   be used with types which are intended to be implicitly constructed into other
  *   other types before being assigned to variables.
  * MOZ_REQUIRED_BASE_METHOD: Applies to virtual class method declarations.
  *   Sometimes derived classes override methods that need to be called by their
  *   overridden counterparts. This marker indicates that the marked method must
  *   be called by the method that it overrides.