Update changelog

Author: ia0

riscv-rt/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Ensure the `.heap` section is 4-byte aligned
 - Limit rustc cfg flags to `riscvi`, `riscvm`, `riscvf`, and `riscvd`.
 - Temporary use of `RISCV_RT_LLVM_ARCH_PATCH` environment variable to include the
   temporary patch required for avoid LLVM spurious errors.