Update changelog for 0.15.1 release (#36)

* Update changelog for 0.15.1 release

CHANGELOG.md

@@ -4,11 +4,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [0.15.1] - 2020-03-01
+
+### Added
+- Optional `max_buffer_size` parameter to `tcp_input` operator ([PR35](https://github.com/open-telemetry/opentelemetry-log-collection/pull/35))
+- TLS support to `tcp_input` operator ([PR29](https://github.com/open-telemetry/opentelemetry-log-collection/pull/29))
+
+### Fixed 
+- Data race in syslog parser ([PR32](https://github.com/open-telemetry/opentelemetry-log-collection/pull/32))
 
-### Changed
-- Added TLS support to `tcp_input` operator
-- Added optional `max_buffer_size` parameter to `tcp_input` operator
 
 ## [0.15.0] - 2020-02-25