Add changelog entry

Author: mitsuhiko

CHANGELOG.md

@@ -6,6 +6,9 @@ All notable changes to insta and cargo-insta are documented here.
 
 - `Filters` is now constructible from `IntoIterator`.  #400
 
+- Change `std` macro calls to be fully qualified.  This fixes issues where
+  the prelude was not used or the macros were overridden.  #469
+
 ## 1.37.0
 
 - All macros for file snapshots should now handle trailing commas (but not yet inline snapshots)