Update CHANGELOG w/ v2.0.0 notes

CHANGELOG.md

@@ -1,3 +1,17 @@
+## 2.0.0 (Unreleased)
+
+As we near certification readiness, we've made lots of changes to the provider. Backwards incompatible changes have been made to the Incap Rule resources. Please review the documentation. Changes below:
+
+* All acceptance and unit tests now pass. There was a race condition issue with dependencies - see this Hashicorp issues: https://github.com/hashicorp/terraform/issues/23169 and https://github.com/hashicorp/terraform/issues/23635
+* Migrate `resource_incap_rule` to use APIv2. See updated documentation and example files for the latest resource spec.
+* Add fixes for data center and data center server result codes (oscillation between strings and ints)
+* Fix importing of various resources: data center, data center server, Incap Rule, etc.
+* Fix ceriticate argument requirements (thanks @areifert)
+* Added GitHub workflow integration for side builds prior to certification (thanks @pklime2)
+* Upgrade to Terraform v0.12
+* Migrate to standalone Terraform SDK
+* Started to improve consistency of error log messages (Site IDs, Rule IDs, etc.) 
+
 ## 1.0.0 (Unreleased)
 
 Initial release of the Incapsula Terraform Provider.