Update CHANGELOG.md

Author: paddycarver

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 2.2.0 (Unreleased)
+
+FEATURES
+* Updated to use the new [`terraform-plugin-go`](https://github.com/hashicorp/terraform-plugin-go) library as a foundation for the SDK, enabling it to be used with [`terraform-plugin-mux`](https://github.com/hashicorp/terraform-plugin-mux) [GH-630]
+* Added the `TestCase.ProtoV5ProviderFactories` property to allow testing providers created with `terraform-plugin-go` with the `helper/resource` test framework.
+
 # 2.1.0 (October 27, 2020)
 
 FEATURES