Add 0.2.1 release notes [skip ci]
# Changelog
## [Unreleased](https://github.com/MarquezProject/marquez/compare/master...HEAD)
+
### Added
+## [0.2.1](https://github.com/MarquezProject/marquez/releases/tag/0.2.1) - 2019-04-22
+
+### Changed
+
+* Support dashes (-) in the namespace name
+
## [0.2.0](https://github.com/MarquezProject/marquez/releases/tag/0.2.0) - 2019-04-15
### Added
