Update CHANGELOG for 3.21.1.

Author: LawnGnome

CHANGELOG.md

@@ -13,6 +13,14 @@ All notable changes to `src-cli` are documented in this file.
 
 ### Added
 
+### Changed
+
+### Fixed
+
+## 3.21.1
+
+### Added
+
 - The `published` flag in campaign specs may now be an array, which allows only specific changesets within a campaign to be published based on the repository name. [#294](https://github.com/sourcegraph/src-cli/pull/294)
 - A new `src campaign new` command creates a campaign spec YAML file with common values prefilled to make it easier to create a new campaign. [#339](https://github.com/sourcegraph/src-cli/pull/339)
 - New experimental command [`src validate`](https://docs.sourcegraph.com/admin/validation) validates a Sourcegraph installation. [#200](https://github.com/sourcegraph/src-cli/pull/200)