provider/aws: Add entry to changelog to note backwards incompatibilty (…

…#6876)

* provider/aws: Add entry to changelog to note backwards compatibilty with AWS Instance

* update wording

* s/using/managin

CHANGELOG.md

@@ -6,6 +6,11 @@ BACKWARDS INCOMPATIBILITIES / NOTES:
  * The `terraform plan` command no longer persists state. This makes the command much safer to run, since it is now side-effect free. The `refresh` and `apply` commands still persist state to local and remote storage. Any automation that assumes that `terraform plan` persists state will need to be reworked to explicitly call `terraform refresh` to get the equivalent side-effect.
  * The `concat()` interpolation function can no longer be used to join strings.
  * `openstack_networking_subnet_v2` now defaults to turning DHCP on.
+ * `resource_aws_instance`: EC2 Classic users may continue to use
+ `security_groups` to reference Security Groups by their `name`. Users who are
+ managing Instances inside VPCs will need to use `vpc_security_group_ids` instead, 
+ and reference the security groups by their `id`. 
+ Ref https://github.com/hashicorp/terraform/issues/6416#issuecomment-219145065
 
 FEATURES:
 

website/source/docs/providers/aws/r/instance.html.markdown

@@ -49,7 +49,7 @@ instances. See [Shutdown Behavior](https://docs.aws.amazon.com/AWSEC2/latest/Use
 * `key_name` - (Optional) The key name to use for the instance.
 * `monitoring` - (Optional) If true, the launched EC2 instance will have detailed monitoring enabled. (Available since v0.6.0)
 * `security_groups` - (Optional) A list of security group names to associate with.
- If you are within a non-default VPC, you'll need to use `vpc_security_group_ids` instead.
+ If you are creating Instances in a VPC, use `vpc_security_group_ids` instead.
 * `vpc_security_group_ids` - (Optional) A list of security group IDs to associate with.
 * `subnet_id` - (Optional) The VPC Subnet ID to launch in.
 * `associate_public_ip_address` - (Optional) Associate a public ip address with an instance in a VPC. Boolean value.