Add changelog

Author: landonxjames

.changelog/crc-fast-feature.md

@@ -0,0 +1,10 @@
+---
+applies_to: ["client", "aws-sdk-rust"]
+authors: ["landonxjames"]
+references: ["aws-sdk-rust#1291"]
+breaking: false
+new_feature: false
+bug_fix: true
+---
+
+Removing the `optimize_crc32_auto` feature flag from the `crc-fast` dependency of the `aws-smithy-checksums` crate since it was causing build issues for some customers.