Update pending change log with merged changes

Adds #2674, and #2677 to pending change log.

CHANGELOG_PENDING.md

@@ -1,5 +1,9 @@
 ### SDK Features
 
 ### SDK Enhancements
+* `aws/session`: Add Assume role for credential process from aws shared config ([#2674](https://github.com/aws/aws-sdk-go/pull/2674))
+  * Adds support for assuming role using credential process from the shared config file. Also updated SDK's environment testing and added SDK's CI testing with Windows.
+* `aws/csm`: Add support for AWS_CSM_HOST env option ([#2677](https://github.com/aws/aws-sdk-go/pull/2677))
+  * Adds support for a host to be configured for the SDK's metric reporting Client Side Metrics (CSM) client via the AWS_CSM_HOST environment variable.
 
 ### SDK Bugs