Update CHANGELOG.md

Co-authored-by: Vadim Kaushan <admin@disasm.info>

riscv-rt/CHANGELOG.md

@@ -38,3 +38,4 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 [Unreleased]: https://github.com/rust-embedded/riscv-rt/compare/v0.7.1...HEAD
 [v0.7.1]: https://github.com/rust-embedded/riscv/compare/v0.7.0...v0.7.1
+[v0.7.0]: https://github.com/rust-embedded/riscv/compare/v0.6.1...v0.7.0